Mustard Algae???

[chem geek]

I didn't realize poly quat was primarily for maintenance, so that would clarify why it did not clear up the algae bloom.

I'm going to try shocking to 20 again and keeping a closer eye, I was only bringing it up to 25 once a day at night, so maybe that's why it didn't clear up all the way, plus I suspect I didn't get the algae completely off the ladder, another reason it may have returned. We're taking the ladder out as well to see if this helps.

Yes, the PolyQuat in the presence of lots of algae will generally be overwhelmed (i.e. get used up) which is why it's much better as a maintenance item while chlorine is the true algae killer when you've got a lot of it. Also, high chlorine levels will get consumed by PolyQuat and the PolyQuat will get converted into another form (essentially broken into pieces and not so "poly") that is still somewhat effective so bottom line, use PolyQuat at the END of a chlorine shock session after the chlorine levels have dropped to "normal" and for maintenance.

Yes, if you only had your FC at 25 at night, then it is quite likely that the FC dropped by as much as half by the end of the day due to sunlight. That would allow the algae to regroup, so to speak. You've got to maintain the minimum of 20 ppm FC throughout the day so if you start with 25 ppm at night, check it in the morning, add chlorine as needed, and again later in the day, if possible. If you are away at work, then test and add more chlorine as soon as you get home. If there was any way for you to even partially shade your pool to prevent chlorine loss from sunlight, then that would be good (even putting in floaters or other opaque objects would be helpful).

Also, keep your pump running continuously during this process to ensure good circulation.

I'm crossing my fingers that the main problem is that you just didn't keep the FC up high enough consistently, but you'll still have to have some sort of algicide maintenance to do after you've killed the algae and we haven't really figured out what will keep this stuff at bay (yet).

Richard