Black Algae

by Christi S.
(Houston TX)

I know, black algae is like herpes...

My husband and I are seriously considering your suggested chlorine and ammonium hydroxide combo to get rid of our black algae, like a 1-2 punch, but I have a few questions. We have gotten rid of it before, pretty recently, then, we went on vacation.

Well, it's back with a vengeance and I just want to burn the heck out of it!

Our 16,500 gallon salt water pool is surrounded by flagstone and lots of plants and trees (and I know now that the salt water and natural stone with our white plaster is a terrible combo, the wash off from the stone is bonding with the plaster, but that's a whole other issue). By the way, our chlorine generator is broken, so I've been manually adding liquid shock for quite some time.

How much of each chemical should we add for our size pool? What will it do to our plants and stone, if anything? Will it be so bad that we need to warn the neighbors? We have a cartridge filter, are there any precautions we should take? Is ammonium hydroxide the same as household ammonia?

And where do we purchase large quantities of ammonium hydroxide anyway?

Thanks, Christi

Thanks for the question Christi

One quick side note; I don't what it is about girls named Christi from Texas but you're the 5th one with the name Christi from Texas that I've answered questions for...

Black algae is one of those that will just keeping back. You might want to look into a good black algae algaecide.

For a 16,500 gallon pool, that chart says to raise the chlorine level up 10ppm you'll need 2 gallons of sodium hypochloride (liquid chlorine) or 3 1/4lbs. of calcium hypochloride (granule chlorine).

Adjust Your Swimming Pool Chlorine..Chemistry..Salt Water Maintenance..Inground

For your pool you'll want to raise the chlorine level to an insane amount, around 40ppm - 50ppm. This is what needs to be done in order to get rid of the black algae problem.

1/2 - 3/4 of a gallon of ammonium hydroxide should do it for your pool.

Black algae is unlike other kinds of algae because it has "roots" and "layers" and these roots and layers will dig into the plaster, so you need to really give it a good shock.

Regular ammonia is just a diluted version of ammonium hydroxide. You can simply Google ammonium hydroxide to find it.

You can try this site. I copied and pasted this right from the window:

www.coleparmer.com/catalog/product_view.asp?sku=8696970&pfx=

I'm not aware of anything that it might do to your decorative stones that the salt hasn't already done. The plants are another story. It really depends on how close they are to the pool and if the pool water gets on them. If you're unsure of using ammonium hydroxide, just do a good chlorine pool shock.

Ammonium hydroxide has about twice the amount of active ingredients than regular ammonia so you need to take precautions when dealing with it. Gloves, goggles, long pants and shirt are a must.

Your cartridge filter should be fine, Just be sure you clean is out as often as possible, maybe even once per day. Have some extras on hand so the switch can be done quickly.

After you kill all of the black algae, you can drain 1/3 - 1/2 of the pool water, re-fill, then re-balance the chemicals once more.

I would encourage you to get a Taylor Reagent FAS-DPD K-2006 pool water test kit. It's the best on the market and the one I used when I did pools in Arizona and now at the Y.

Water Testing Kit..FAQ..Chemistry Testing..Procedures..Balance..Swimming..

Hope this helps and let me know how it turn out for you

Robert

Donation..My Pool Guy..