Algaecide Overdose

by Jeff

I have read several of your posts regarding algaecide overdosing. I believe I overdosed my pool with dimethyl benzyl ammonium chloride (from Dupont) at the end of the summer season.

It is now 2 months later and my spa (which is designed to overflow into pool ) foams up 6 inches every time I turn on the air pump and there is a distinct odor (not foul but much different then the usual chlorine odor). All readings for chlorine/free chlorine/ph and alk are in line and the pool is crystal clear. The pool temperature has dropped significantly during this time. My pool guy also uses an enzyme treatment.

I now know by reading your posts of your suggested algaecides. My question is what can I do about it now that I am in this situation. I tried an anti-foaming agent but it did not fix the problem. Is there anything more to test, add or do I have to drain?

Thanks for the question Jeff

This visitor used the same kind of algaecide you used and got the same results, foaming water. I always recommend using a PolyQuat 60 algaecide as others do tend to foam. Many of the lesser algecides use copper as their base. You're adding metal into the water.

If your chemicals readings as good - chlorine at 1.5 - 3.5ppm, pH 7.4 - 7.8, TA 80 - 100ppm, hardness 150 - 250ppm, and CYA 30 - 50ppm, there's really no reason to use an algaecide. If you can't take weekly readings due to a busy schedule then I'd recommend using a PolyQuat 60, but under normal circumstances and about 20 minutes per week of work on your pool, there's no reason to use an algaecide.

Algaecides are meant to break down over time but an overdose can take longer to dissipate. It depends on how much was put in. Shocking the pool can help the algaecide break down faster. To help the process along ever faster, you can do a 1/2 drain and refill, but then you'll need to allow for 8 - 10 hours of filtering, retest everything, then balance the pool again. I'd also shock at this point.

To the best of my knowledge there's no chemical to remove the algaecide. So basically you can keep backwashing and topping the pool off, allow it to dissipate naturally (which will take some time), or do a 1/2 drain the refill.

If you have a heated hot tub and want to use it quickly and if it was my pool, I'd opt for the 1/2 drain. If you're not in a hurry to use the pool or can't due to the cooler temperatures, then backwashing and topping it off would be the way to go.

If you need immediate assistance (within 24 hrs) or for emergency personal assistance, you can make a donation of your choice and I'll answer your questions by phone.

Contact Me


Hope this helps.


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Over Dose of Copper Based Algaecide

by Howard Forbes
(Peoria Il.)

The guy that normally closes my pool instructed me to use 2 bottles of copper triethanolamine complex. After I blindly added it I read the bottle and said to use only 4 oz.

I am afraid that at that concentration when I open the pool in 7 months it will be a health hazard. Pool was drained to half around 7500 gallons.

Using hth test strips. At the time of closing pH was 7.4, Chlorine around 5, alkalinity 100 and CA 50. What would be your recommendation for this mistake.

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