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copper sulphate as Swimming Pool Algae Remedy?

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Q. After a few months of clear water with copper treatment, I am now having a bloom of a copper resistant green filamentous algae. My copper concentration is 0.4 ppm as determined by the LaMotte 3619 Copper Test Kit. pH is maintained under 7.4.

It's been going on for a few days now with no sign of abatement.

I do have a residual, from the previous Chlorine system, of 150 ppm Cyanuric Acid, i.e. stabilizer. Also when I a add more copper sulphate, I don't see a rise in concentration beyond the 0.4 reading which has me puzzled. Could it be the residual CYA?

I read about a copper resistant green filamentous algae so I guess I have it.

What should I do?

John Stranahan [returning]
- Miami, Florida USA
January 14, 2018

A. Sounds like you've got a nasty algae there.

First off, I'd reduce pH to 7.2 or 7.1 This will make the copper more soluble and more effective.

Then I'd hit it HARD with chlorine, calcium hypochlorite, until you get up to 4 or 5 ppm which stays up overnight. If you pool is heavily infected, you will likely have to make multiple adds over a few days. If yours is a typical 16' X 32' pool, you might end up using 5-10 pounds or more of hypochlorite. As you kill it off, keep back washing your filter to get rid of the dead stuff.

Consider NOT using CNA. In my opinion it causes more problems than it solves.

You CAN kill it.

Rereading your post - "the previous Chlorine system".

By this do you mean that you entirely stopped the use of chlorine and relied only on copper?

If so, that's wrong. Copper is highly effective against MOST forms of algae, but not all. And copper is ineffective against other possible nasties - bacteria, viruses, odors and others.

Chlorine is absolutely a necessary component. It should be about 1 ppm at all times, with an occasional boost to 2 or 3 ppm.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

thumbs up sign Solved for the time being.

Thank you Jeffrey for your interest and comments.

This situation came about from the pool owner (I've offered to help her with the pool care) having used trichlor tabs exclusively for chlorine titer. Like with so many that I have read about online, the cyanuric acid (stabilizer) in the tabs builds to problematic concentrations. It remains as the chlorine diminishes. She is adamant about not draining half or more of the pool to reduce the CYA concentration. At the present concentration of 150 ppm, chlorine action is reduced dramatically, requiring very high chlorine concentration for control.

Since the pool is solely ornamental during the winter and since it is only she who uses the pool occasionally in the summer, pathogens are of no concern now and human contagion never.

So I thought that I would give "copper only" a try by using copper sulphate [this product on eBay or Amazon affil links] as available economically as root killer at Home Depot and Lowes. At 0.3 to 0.5 ppm copper it cleared the pool of algae after Hurricane Irma and did well until I got a copper resistant strain a few weeks ago. It is consistent the online description of the copper resistant Pithophora, a green filamentous algae.

Knowing that copper is allowed in drinking water up to 1 ppm I decided to see if I could get some algaecide action at 1 ppm since it is still safe for humans at that level.

After three days at 1 ppm copper the pool is now clear. The plan is to now maintain the copper concentration at or a little under 1 ppm.

When the season rolls around for her occasionally using the pool I will sanitize it to 1 ppm chlorine for pathogens.

So for now all seems to be in order. I've read the warnings about the black stains resulting from chlorine copper interaction but that is to be seen or not.

BTW, the patches of black algae on the pool wall have disappeared since using copper sulphate, without any scrubbing.

John Stranahan [returning]
- Miami, Florida USA

Q. After deliberately increasing the copper concentration to 1.4 ppm to kill off a resistant strain of algae I now need to reduce that concentration to below 0.5 parts per million to get the pool ready for swimming season.

What I am looking for is a low-cost method of decreasing the copper concentration. Methods available via pool supply stores cost over $100. I'm hoping to find something lower in cost and PROVEN to work in swimming pools with common pool filtration systems. Any information on this would be greatly appreciated.

Jon Stranahan [returning]
- Miami, Florida
May 17, 2018

A. We have an 18' round 54" deep above-ground pool. Every summer we only buy three things …

We already have a small box of copper sulphate we bought at our local tractor stuff store. We mix 1-1/2 cups of the bright blue granules in a 5 gallon bucket of clean water. Stir until all grains are dissolved. We walk the perimeter of the pool in the afternoon and pour all of the mixture in. Then (here's what we buy) we walk around again pouring 5 gallons of HOUSEHOLD bleach [adv: bleach/sodium hypochlorite in bulk on eBay or Amazon affil links] . The cheap stuff works for us but don't use laundry bleach. It has less chlorine in it. After adding 2 chlorine tabs (3") to the floaty thing. We wait usually 2 days with the pump on full time. Backwash and rinse our sand filter 2x per day.

By then the water is blue but still can't see the bottom. A trip to the "garden and pool" center at the local WALL place for a bottle of clarifier. This coagulates (clumps together) the now dead algae and brings it to the surface so the filter can more easily filter it out. We walk around the pool pouring straight from the container about half of the thick blue liquid. Again keep the pump constantly running. A day or two later we can usually see the bottom and all the muck. Once we vacuum, this stirs up more stuff (we vacuum while in pool) after that we use the rest of the clarifier in the same manner as before.

Don't get in the pool if the water is green. This could be live algae and getting it in ears, nose or mouth could cause problems. Don't use any more copper sulphate. You can test it if you want but we find our measurement works for us. We only use one dose of copper sulphate upon opening the pool. Only once did we use it twice because we had a very very rainy summer, weren't in the pool often and let the chlorine tabs run out. We haven't had any blond haired beauties turn green on us. We don't use shock either. If you use too much clarifier it could make pool a "white" cloudy. But it will filter in a few days. We are usually vacuuming at 4 days and are swimming about 7 days after starting the routine. We use the recommended dose on the box of copper sulphate for the gallons we have. Use the internet to figure your gallons if you don't know. Have been using this in our above ground with the original liner for 15 years. We do have a sand filter but no ionizer or UV filter or heater. So I don't know if you should use with these. Hope this helps.

Judith Brewer
- Hohenwald, Tennessee, USA

A. Jon Stranahan: Your Cyanuric Acid is three times the ideal maximum. It should be 30-50 ppm (the lower, the better, if you can get away with that in Miami). If you are using chlorine, then it isn't doing anything at all at with 150 ppm Cyanuric Acid.

Joe Schmuccatelli
- Tampa
May 21, 2023

Q. I have now used Aqua Pro 'Algaecide' 2 liters in my 63000 liter pool, it is clearing up and getting blue again. My question, however, based on the previous posts, is whether one can maintain the Algae with the 'Copper sulphate' powder one can buy at the Chemist. Can anyone advice how much to use and timetable?

Manfred van der Brugghen [returning]
Construction Professional - South Africa, Johannesburg
January 19, 2018

A. Maybe you can use plain copper sulphate, but its solubility is limited. IF you keep your pH on the low side, say 7.1, it may be soluble enough.

Much better to buy chelated copper sulphate based algaecide which is freely soluble. It doesn't need to be expensive since it is essentially permanent, being lost only when you remove water.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

thumbs up sign Thanks Jeffery, will give it a try.

Manfred van der Brugghen [returning]
Construction Professional - Johannesburg, South Africa

A. In fact, copper sulphate is very easily soluble. Prior to dispersing into the pool water it is good to add half of a cooking ladle of CS (ca. 150 gr) into a bucket with water (ca. 10 l), and mix it. Then, taking out continuously the dispersed solution from top and distribute it into pool while filling up more water into bucket and mixing, taking out again, etc., until all the blue powder is dissolved.

Jan Mrskos
- Lampang, Thailand

Q. My situation: Hi, we used copper sulphate in our 27' round, 4 1/2'deep pool. My question is, what can I use to raise the hardness, total chlorine and free chlorine? They are all showing 0 on my test strip and I don't think I can use shock.

Jan George
- Tyrone, Pennsylvania
July 2, 2018

A. No worries about Copper Sulphate, the pentahydrate (CuSO4·5H2O), the most commonly encountered salt. Copper (Cu) is allowed e.g. in German standard for drinking water up to 2 ppm. And Cu is contained in CS just by 20 - 25%, i.e., with 8 - 10 ppm CS you get 2 ppm Cu.

During next days the Cu is depleted by reactions with algaes and other unwanted substances in pool water, hence it will be filtered out, backwashed and vacuumed from pool bottom.

And/or farther dissolved by rainwater, by additional water after backwashing, vacuuming.

After CS dissolving it is better to stop the pump and let the CS work. When later added a flocculant (e.g. Alum - a wonderful substance formerly used by our fathers for stopping bleeding after shaving), all will sink to bottom.

BTW, the algaes are not harmful, they just keep the water from being crystal clear, beautiful for our eyes.

Jan Mrskos
- Lampang, Thailand

Q. Hi. I need to know how much copper sulphate to add to drinking water to remove Algae and I believe any protozoans or coliform bacteria which I also believe are sensitive to CuSO4?
My storage tank is 5000 Litres.
i.e., how many grams to 5000 Litres.

Many thanks.

Jean-Pierre FOURIE
- Harare, Zimbabwe
November 16, 2018

A. Hi Jean-Pierre. Garry S claimed that 1 ppm ^ copper is quite safe, and estimated that ^ at 0.5 ppm 100-120 grams ^ copper sulphate would be required for a 50,000 litre pool (meaning 10-12 grams ^ copper sulphate for 5000 litres). Jan M says 2 ppm ^ copper is safe per German drinking water standards. The USA EPA limit is 1 ppm ^ copper. WHO seems to accept 2 ppm but lean towards 1.

This should cover it if you're talking about your own family's drinking water. If you have public responsibility for other people's water I think you need to work on a deeper level with regulatory agencies.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

thumbs up sign Ted Mooney, P.E. RET : Thank you so much for that information. That's exactly what I required. The promptness of the answer was impressive. Thank you again.

Jean-Pierre FOURIE [returning]
- Harare Zimbabwe

The 1 or 2 ppm is a limit of Cu for drinking water. Since CopperSulphate contains only 20 - 25% of Cu, the limit for CS can be 4 - 5 ppm (when Cu 1 ppm), event. 8 - 10 ppm (when Cu 2 ppm).

Jan Mrskos
- Lampang, Thailand

thumbs up sign  Thanks, cousin Jan. Garry S suggested 0.5 ppm of copper for algae control and said that it equated to 100-120 g for a 50,000 liter pool and his calculation was correct and based on your copper percentage of 20-25%. For Jean-Pierre's 5,000 liter water tank, that would scale down to 10-12 g, so hopefully we gave him the answer he sought.

But you are correct that my posting was confusing in 2 ways --
-- not making clear which numbers referred to copper and which to copper sulphate (which I have now repaired with superscripts, and
-- reverting to Garry's 0.5 ppm of copper for the calculation while saying 1-2 is probably okay. Thanks for the catch.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. I have just started to use copper sulphate to try to keep my tile joints clean after spending 4 days cleaning them by wire brush and gaining aches and pains in the process. I note that people are talking in terms of PPM, but how is this measured? Is it simply the number of grams of CS granules divided by the total number of grams of pool water x 1 million?

David Ballinger
Retired civil engineer - Pattaya, Thailand
February 14, 2019

A. Hi David. You are right about PPM meaning parts per million, but uncertainty is introduced when you ask a 3rd party what someone else meant :-)

Some people might mean parts per million of copper (Cu), others might mean parts per million of copper sulphate (CuSO4), and some might mean parts per million copper sulphate pentahydrate (CuSO4·5H2O = weight of the crystals).

copper sulphate pentahydrate is 25.5% copper by weight, so if you want 1 PPM of copper you need to add 4 PPM of crystals. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

thumbs up sign  Thanks to Ted for his very quick response to my query. An on-line pool supplier in Thailand recommends that CS should be added at 3 gm per cu.m. of pool water. A cu.m. of water weighs 1 million grams so based on the above recommendation the proportion of CS in solution will be 3 parts per million, producing slightly less than 1 ppm of copper. The recommendation goes on to say that this treatment should only be done twice per year to avoid build up of copper with its undesirable side-effects.

David Ballinger [returning]
- Pattaya, Thailand

A. Once you are frequently backwashing the filter and vacuuming the bottom (I do it mostly in one go) you have to add fresh water. Consequently, the concentration of the Cu is slowly reduced. And that beside the fact, that the Cu is also diminished by reacting with the algaes. Therefore a timely addition of a new CS portion is needed, especially in the springtime.

As a matter of fact, when e.g. the German standards for drinking water allow 2 ppm of Cu, the 2 ppm in the water for swimming should not make any harm, even if it is a bit over. The 2 ppm does not mean that a tiff or two of it is poisonous, the value is for a precaution if it would be permanently drunk over a longer period of time.

With treating the swimming water by CS we spare ourselves of the daily hassle with keeping a high level of chlorine (to kill the algaes) and also of the difficult (and expensive) job of maintaining of the pH, that is for the chlorine effectivity important but not for the CS.

Jan Mrskos
- Lampang, Thailand

citric acid as chelating agent in swimming pool

Q. Hi I read that you can use citric acid as chelating agent -- what would the ratio be? I have a 50 000 ltr pool. Pardon the ignorance but what does the chelating agent do, and will it not diminish the effectiveness of the copper sulphate. Thank you.

Rassie Erasmus
- Amanzimtoti Kzn South Africa
May 22, 2019

A. Rassie,
In chemistry, metal ions dissolved into water carry a positive charge, because they are missing electrons compared to their solid metallic state. This means that other ions with negative charges like to stick to them. When this happens, it's called a ligand. The more electrons "missing" from the metal ion, the more ligands can stick to it. Similarly, some negatively charged ions carry multiple negative charges, and some of these are structured in a way that they can sort of wrap around the metal ion and act as several ligands all in one molecule. When this happens, the ions stick together much more strongly than with individual ligands. This is known as chelating, taken from the Greek word for claw, because it sort of looks like a claw gripping the metal ion.

However, I don't know how this specifically applies to a swimming pool. If you're using copper as a disinfectant, I'm guessing you don't want it chelated because that might protect the germs from the copper. "Chelation therapy" is one method used to protect people that have swallowed toxic metals.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

Q. Thank you Ray: Read that chelating the copper sulphate with citric acid slows the process down and would give you more control over its use as disinfectant(algae) in pool water treatment.would I be wrong in thinking that the chelating of the copper sulphate would keep it in "suspension" until needed.Treated a friends pool with Gary Sutherland's formula after he spend hundreds on pool chemicals (so cheap,did it for is I now have friends I don't even know but do recognize the fact that misuse of the copper sulphate is dangerous. The pools I have treated shows levels of 0,80 0,5 and 1,0 and according to local pool companies the acceptable level is 0,2. Any further advise on the use of copper sulphate for pool treatment would be apreciated. Thank you

Rassie Erasmus
- Amanzimtoti Kzn South Affrication
June 4, 2019

Q. Hi Everyone, We have a concrete 90 year old in-ground pool. It is approximately 84,000 gallons.
Our care is to drain the pool in the spring and wash down the sides and bottom with power washer. We fill the pool from the spring.

This has always worked, but last year and this, I had 2 high school boys drain and clean. When the pool filled, it was slightly green and cloudy. I shocked it, but it didn't help. This year, again the same problem, but the algae is worse. I triple shocked and nothing. I am going to use copper sulphate, now. I think that the pool just wasn't cleaned properly. I had always power washed scrupulously in the past. WE HAVE NO FILTER. Water runs into pool from a small warming pool. Water can be diverted to pond to somewhat warm the big pool. Our pool is so untraditional that I simply can't find any solutions. There is no electricity down at the pool about 200 yards from the main house. Any thoughts truly appreciated. Also, My usual treatment was to toss in a couple of cups of granular chlorine, every other day. This kept the pool clear and when water diverted to pond; the chlorine dissipated and didn't harm fish. I ran this by our local fish and game and they said the sheer volume of water in the pool mixed the chlorine with little harm to the fish, frogs, etc. in the adjacent pond. Thanks to all.

Frannie Stone
- McDonald, Pennsylvania, USA
June 27, 2019

A. If the chlorine is granulated then it is obviously organic one with addition of cyanuric acid for stabilizing against UV radiation, prolonging the chlorine effectivity (long term effect). However, the CYA does not evaporate like the chlorine. Once the water is not much replenished, the rising CYA value will reduce the chlorine effect.

Unlike the cheaper inorganic chlorine without the stabilizers, however, without the unwanted problems. As a powder it can be dissolved in a bucket and dispersed into pool water every 4 - 6 days or so.

Jan Mrskos
- Lampang, Thailand

A. Copper (Cu) allowance for drinking water in majority of countries is 2 ppm (2 mg/liter). If used a copper sulphate(CS - cheap and easily soluble) that contains 20 - 25% Cu, the content of CS can be 8 - 10 ppm, i.e., 10 gr on 1,000 L (1 m3).

Jan Mrskos
- Lampang, Thailand

A. Your green tinged water may not be an algae problem at all. Next time, try raising the alkalinity aggressively to see if the water turns clear. It might work best if you first lower the ph well below 7 for a day. Be aware of ph of saturation index so you don't go too far out of balance for too long, which will cause other problems.

Carl Edwards
pool maintenance - Lynnwood Washington

Q. Hello,
I just started using a solar powered floater in my swimming pool with a copper anode (Maybe solid copper, maybe not). This results in much less chlorine usage and really prevents algae from forming in the pool. I have to clean the anode with a wire brush each week to get rid of the oxidation/corrosion. Would you please explain how this works to keep the pool clean and what can be used to clean the anode without much wire brushing (vinegar, etc). Thank you.


Khan Kesselman
- Bridgeport, West Virginia USA
June 3, 2020

A. You can simply add water soluble copper salts (i.e., copper sulphate), and ditch the copper anode.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

Q. My pool holds 125,000 gallons of water; the pool is cement.
I have an out of control algae bloom. I purchased copper sulphate but do not know how much to use, also do I mix it with water or broadcast it over the surface. Also, how long do we need to wait after using it to safely use the pool.
Thank you any thing you can tell me is much appreciated

Ellori B. [last name deleted for privacy by Editor]
- Windsor Ontario Canada
June 17, 2020

A. Hi Ellori. I appreciate you detailing exactly what your problem is, and providing the size & material of construction of your pool, and I hate to be unhelpful :-(   ... but starting over causes threads to grow to impenetrable length, while launching duplicative ones makes the challenge of finding the answers much harder :-)

So please study the thread and try to challenge an assertion, ask for clarification of something that has been said, or explain what you think is different with your situation. Thanks!

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. OK, I now know how much copper sulphate pentahydrate to add to my pool for a given concentration but my question is: How much, in PPM, is necessary to keep the algae at bay? I have insignificant algae at this point in my 30,000 gallon cement/plaster pool. I should be adding around 500-1000 g of the agent above for 1-2 PPM.

Stephen Hobrecht
- Los Altos, California
July 18, 2020

A. Hi Stephen. Others readers seem to have claimed that 0.5 ppm may be enough, but seems very 1-2 ppm safe. 30,000 gallons is about 114,000 liters, so 500 g of copper sulphate pentahydrate would be 0.5/114000 = 4.4 ppm of that material or 1.1 ppm of copper. It sounds like 500 g should be right and 1000 g would be more than needed.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

thumbs up sign Ted, thank you for the VERY quick response to my question. I could tell that this is the correct place to ask because of the thorough understanding of pool chemistry that is exemplified by the answers to the many questions in this forum.

Stephen Hobrecht [returning]
- Los Altos, California

How often must I re-add copper sulphate to my pool?

Q. Hi everyone,

Great discussion with lots of helpful info!

So I've decided to give copper sulphate a go in my pool, but I do however have a question or two.

Say I were to treat the pool according to the required dosage for how long would the copper sulphate solution stay in the water?

For example if I add 160 grams of copper sulphate to a 40 000 liter pool which equates to 4ppm, how often would I have to add copper sulphate to basically maintain this ppm level and keep the pool algae free?

Your advise would be greatly appreciated.

Stefan Vermaak
- Johannesburg Gauteng
August 5, 2020

A. Limit of Cu for drinking water is 1 up to 2 ppm (Germany). But when we use the copper sulphate that contains just 20 - 25% of Cu, the ppm can be 8 - 10. And the Cu limit does not mean that it will poison us, it just would not be good for drinking over a longer time period (but we do not drink the pool water, do we? (almost).

There are some measurements for the Cu content (in fact, I have never seen one). I am observing a growth of algae in the gaps between the tiles (in my case). And when there is a lot of rain and/or a lot of new added water after bottom vacuuming and filter backwashing, it needs new dosage. The CS is consumed by the algae marriage, going away with the filtering, backwashing.

It's better to foresee the dosage before the water starts to get greenish, otherwise after the CS addition the water will start to be milky, it will take few days and frequent backwashing to get it clear again. Better to make it in small dosages more often, to avoid a foaming that occur sometimes, also an oily surface can appear - depends on the purity of the CS.

In general, there is no great danger of overdoing as sometimes the pool shops try to scare of the CS. It's much cheaper, much easier and even much healthier than relying on chlorine only and there is no need to care about the pH level (no influence on the CS effect).

Jan Mrskos
- Lampang Thailand

A. This is an example of how much copper sulphate to use in a pool and stay below 0.5 PPM.

Taking weight ratio, 1 kg. of CuSO4 releases (63.546 g/mole Cu) / (159.61 g/mole CuSO4) = 0.405 kg. of elemental copper in the pool water. To achieve a target of 0.5 ppm of elemental Cu in 100,000 liters of pool water 0.05 kg. elemental Cu is required.

Therefore, the required dose of CuSO4 is (0.05/0.405) = 0.125 kg. for 100,000 liters of pool water.

I would use this to start with. If there is no effect in a green pool to get it clear within a week I would add a similar dose. You're still at 1 PPM, which is safe for health.

- Jakarta
August 12, 2021

Q. Hello ... I have been putting about 350 grams of copper sulphate once a month into our 100,000 litre pool. I use 2 cups of chlorine powder for the other 3 weeks of the month. We have always had crystal clear water. I'm concerned about the possible negative long term health effects from the copper sulphate as it can be absorbed through the skin.

Dave Bradshaw
- Durban, South Africa
November 10, 2021

Q. Hi Okoth, I have been using only copper sulphate (Trussi) and Granulated Chlorine and a floating 3"Chlorine Tab since March.
Now that we are into the rainy season the water is not as crystal clear as before.
Should the pH still be controlled as haven't used HCl since using the Copper/Chlorine method?
Many thanks for any input you may have.

Retired - Bali, Indonesia
December 2, 2021

A. I hope that in the meantime your water has cleared up properly. Of course, in the heavy rainy season the water is more prone to algae growth. Firstly, because the heavy rain will bring plenty of dirt and vegetation dust from the air into the pool water. And secondly, the plentiful water addition dilutes the copper sulphate concentration, the algae will be happy for that. Therefore, in that season the CS has to be more often renewed.

The pH value has (almost) no influence on the CS efficiency. It's just good for efficiency of chlorine in case the chlorine also contributes to reduction of algae growth. But with the CS correct dosage it will be managed. Then, the chlorine serves for killing bad bacteria.

Once the CS dosage has not been strong enough and the water has already started getting green the curing will take few more days with an increased filtering and frequent backwashing. That's why it is advisable to keep a proper CS level continuously, the problem will not happen.

Jan Mrskos
- Lampang Thailand
October 14, 2022

thumbs up sign Thanks for your reply and input Jan. All has been solved and now starting into the next rainy season.

Tom Smith [returning]
- Bali, Indonesia

Q. How much copper sulphate do I need in order to eliminate liver flukes in a communal water dam of 20000 litres of water?

Kasule Barnabas
Veterinary technician - Kampala Uganda
February 8, 2022

Q. Pool of 9 m by 3.2 m, average depth 1.8 m.

How much copper sulphate?

S Brink
- Stellenbosch. Western Cape
December 20, 2022

A. Hi S. Most readers seem to have suggested that 1-2 parts per million of copper is ideal since it's 'drinking water safe'. copper sulphate pentahydrate (the blue crystals) is 25% copper. So about 4-8 parts by weight of crystals per million parts by weight of water sounds about right.
A cubic meter of water is 100 liters, and a liter of water weighs a kilogram, so about 350 grams.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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