What is this exactly?

[rsa777]

Second year I have run into this. Vinyl pool with high chlorine and good PH. Then this shows up. Water is crystal clear. If I touch these up comes a green puf.
I don't understand how this appears if I maintain high chlorine levels. Using BBB. I'll have to shock to kill it. I do have many oak trees in the area. Seems to happen once it gets hot and humid.

 

[duraleigh]

That is dead algae settling to the bottom of your pool. You do not provide enough information to give you an accurate answer but I will say that algae does not grow in a pool that has adequate chlorine.

Can you post a complete set of test results? That will help us give you some educated information instead of just guess work.

 

[robertmee]

Once it gets hot the burnoff of FC is accelerated so unless you adjust your chlorine addition to compensate you could be dipping below the minimum FC levels to prevent an algae bloom.

 

[Catanzaro]

RSA777:

Please add your signature so we can understand your pool better. In a properly chlorinated pool, if I had to take a guess, this is either a circulation problem (dead spots) and/or lack of brushing. Brush twice weekly and if you have great success, you may be able to cut back to one time weekly. Keep us posted and welcome to TFP!