Green powdery algae on bottom of pool

[Jeff618]

My water is clear, I have shocked tested levels etc. I vacuum to waste and the next day there is more green to vacuum out. I keep doing this then a day or two later the same thing. I have not been turning my filter off as I change to waste, filter, backwash etc. can that cause a problem?

[Watermom]

Hi and welcome to the Pool Forum!

We'll need some additional info to be able to help.

1. What kind of pool is it? What is the volume?
2. What size pump and what kind and size of filter?
3. Exactly what all have you added to the pool, meaning ingredients and not just product names like 'shock.'
4. What does the water look like?
5. What is the source of your fill water --- a well or city water?
6. Do you have a drops-based test kit? If so, what kind? Post current numbers.

If you don't have a good drops-based test kit:
The test kit that we think is by far the best is the Taylor K2006 or 2006C (better buy). Not available locally but you can get it through this link that takes you to Amazon: http://pool9.net/tk/

But, in the meantime, go to Walmart and see if they have the HTH 6-Way drops-based kit (no test strips!) and get that. If they don't, get an OTO/Phenol Red kit (yellow and red drops) instead. Use it to test and then post your numbers. Also while you are at WallyWorld, get several jugs of their generic 8.25% bleach, a couple of boxes of 20 Mule Team Borax (laundry aisle) and a gallon of distilled water.

Repost with requested info and then someone here can try and help you.

(Until you registration is completed, you won't be able to see the rest of the forum while you are logged in. So, copy that link and then paste it into a browser window after you log out.)

[PoolDoc]

It sounds like mustard algae, which is the most chlorine resistant form of algae.

You'll need to raise your chlorine level to at least 20% of your CYA level to control it . . . but you have to be able to (a) accurately test your CYA level, and then (b) accurately test chlorine levels above 10 ppm.

Using a phosphate remover can help, since very low PO4 levels slow algae growth, but ONLY if you get PO4 levels below 125 ppb. To accomplish that, you need ANOTHER testkit, to measure phosphate levels. Unless you do this, phosphate removers are a waste of time and money, since lowering PO4 levels from 5,000 ppb (common, with some city water supplies) to 1,000 ppb accomplishes nothing, since 1,000 ppb is STILL more than enough for the algae.

[BigDave]

... I have not been turning my filter off as I change to waste, filter, backwash etc. can that cause a problem?

Do you mean to say that the pump is running when you change the multiport valve selector? You should definitely shut down the pump before moving the MPV.