Algae Contamination in DI Water Tank

A. Hi Michael. Maybe a heater?
Aaron Greenwood suggests in thread 5358 that raising the temperature to 140 °F once a day greatly reduced the algae problem.
Luck & Regards,


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

A. Hiya!

If you go this route, 140-145 °F/ 63 °C is the temperature for Pasteurization, but has to be held at minimum 30 minutes. This is what I use to sanitize my brewing equipment between runs, and prepare the molasses and rotten dunder solution for yeast. It works perfectly on the wide variety of wild yeasts and fungi that colonize that acidic solution; it will definitely kill off the biologicals.

On the down side, that's a lot of extra moisture going into the air, and if your air handling system can't keep up, you're going to trade one problem for another by creating the ideal environment for your walls to grow... stuff.

Source: I've worked at 2 indoor fish farms with insufficient ventilation. The walls were nasty.

You can partially combat this by covering the tanks or using polypro hollow balls (like ping pong balls, but thicker and way more expensive) to reduce the amount of vapor leaving the surface.

A. You may have biological problems, or you may have colloidal tin precipitates in your water. The ability of colloidal tin to pass through a DI system is not unusual; we have seen it many times. You may want to have the water tested for the number of Colony Forming Units (CFU) per 100 ml. If you have a biological problem that you can actually see, they will be too numerous to count! If you have < 100 per 100 ml, then you don't have a significant biological problem.

As far as sanitizing your system, a small amount of peroxide or bleach [adv: bleach/sodium hypochlorite in bulk on eBay or Amazon] (<25 mg/l) will not significantly harm the IX resins provided that the contact time is short. If there is activated carbon before the DI resins, then this will decompose most of it before it gets to the resins. However, if you have a biological problem, then your activated carbon is now probably a breeding ground and needs to be replaced in conjunction with the system sanitization. The IX resins are not usually a significant breeding ground unless there is a long time period between regenerations.

Good Luck!

A. If the pH is climbing in recycled di water after a few days, the problem is likely that there is not enough cation exchange capacity.

As contaminated water passes through a cation column it is acidified (H+ replaces other cations like sodium, copper, nickel, etc.). As the now acidified water passes through the anion column it is neutralized (OH- replaces other anions like chloride and sulphate, then reacts with the H+ to form neutral water).

If the cation column is exhausted it has no more H+ to release and will usually begin to let go of Na+. When the Na+ combines with the OH- from the anion column it makes NaOH, sodium hydroxide, a.k.a. caustic soda [affil links] .

Increase the number or size of cation columns in the system. Then watch out for running out of anion capacity (usually more common)! Best monitoring is to do both conductivity and pH.

A. Hydrogen peroxide will likely be destroyed by ultraviolet treatment, but keep in mind if you have enough dissolved solids in the water to color it, the transmission of the ultraviolet will be adversely affected, thus reducing the effectiveness of the ultraviolet units' sanitary or peroxide reducing qualities.

As mentioned before, be certain you have enough anion exchange contact. DI water has a pH which is neutral or very slightly acidic. Have you considered ozonating the water? Ozone will rapidly oxidize colloidal metals; after treatment with ozone, place a polishing filter (x<1 micron) inline before the ultraviolet unit to keep the water clear; if the u.v. unit is sized correctly for the flow of water, the u.v will effectively destroy the ozone. There are quite a few ozonation & u.v. equipment manufacturers out there who will be happy to help you size the apparatus you need.

It is unlikely algae & bacterial blooms are responsible for your troubles here, as there are not a lot of nutrients available in D.I. water. Add in the oxidizing ozone and the advanced oxidation process the u.v. unit would provide, and your system would be downright inhospitable for aquatic life.