Re-occurring ZOMBIE Algae...

[chem geek]

Yes, that's the right stuff.

[BigDave]

The bottle of Kem-Tek phophate remover I just bought from Amazon is labelled the same as the two I bought in June.

[PoolDoc]

OK, good.

If you have a PO4 test kit, I'd be interested to see how much removal you see for a given dose.

[BigDave]

The data I have so far is uncomfortably soft. I have the Taylor phosphate kit.

From the initial supply bought from Amazon in June, I used about (not measured, guessed) one and a half quarts to get from > 1000ppb to 500ppb. At this point, I added 5 days worth of bleach, covered the pool and went on vacation.

Ten days later I uncovered the pool, FC 12ppm (CYA 60), some appearance of what might be dirt or might be mustard algae in the seams and corners where it usually grows. Allowed FC to come down and maintained 5.5ppm-7.5ppm FC. Added about 1/2 the remainder of the second quart.

Another ten days or so go by with several thunderstorms bringing tree debris into the pool. Definite return of mustard algae. Brush, vacuum, backflush. PO4 now at 250ppb. No makeup water for the three weeks since PO4 measured 500ppb. Added the remainder of the second quart.

So, about 8oz of the (June) Kem-Tek phosphate remover took about 250ppb out of my 7700gal pool. If my math is right, that's a whole lot more like 0.75ppm/10,000gal than 2.0ppm/10,000gal as described on the label. This is of course confounded by the storms, debris, high chlorine and time.

[PoolDoc]

OK. If you can, keep track of it.

I'm beginning to think that the ratings are 'ideal', not real. Adding lanthanum chloride to a pool can form lanthanum carbonate -- which is ALSO rather insoluble.

I believe that, over time, if the lanthanum carbonate remains IN the pool (pool floor or on filter media), it will be converted to lanthanum phosphate. But if you clean the filter before that happens, you'll end up having used a portion of your PO4 remover as an expensive and inefficient way to lower carbonate alkalinity!

[BigDave]

I let it sit on the filter for a long time (3 weeks) before backwash. I'd think that it should have finished.

A couple observations:
It took about three days to clear the cloud with each addition of phosphate remover. That's with the 27" sand filter and moving 40gpm in the sun and 10 gpm all the rest of the time. The cloud was minor, more of a dulling of the pool than a cloud. At night, I could see the beam of a bright, focused flashlight in the water.

When I added the first and second half-quart doses, the pool water smelled strongly like laundry.

After every dose the surface tension appeared to change dramatically - the water looked thick and the roil on the surface near the return was far more pronounced.

I hope to provide better info in August - the beginning of the summer has been crazy for us.

@PoolDoc: I realize this is now prety for off-topic from the original thread. Sorry. It might be a good idea to move it to the previous PO4 remover thread or make a new one to collect observations.

[PoolDoc]

3 weeks should be long enough, if anything is!