Running out of POP!

[sosspenc]

Oops, sorry. FC and TC are 20 CC has been no more than 0.5 for last 2.5 weeks. pH I use a probe for aquariums...it's been calibrated recently. I test cl- using a FAS-DPD titration method; CYA, alkalinity, and acid demand I usually do at work (university lab). I have also confirmed cl- & pH levels at work. I am beginning to think that I'm missing something, or my filter is sick.

Thanks,
Stella

[PoolDoc]

Yes, if you want to try something, add another dose of bleach and then turn your filter off. I want to leave it off for 2 full days.

Here's what I think may be happening. The Tagelus 50 is a shallow bed 21" sand filter. It's rated at 50gpm, but in reality, should never exceed 35 GPM. I'm not sure what 3/4HP pump you have, but if it's something like a Pentair Challenger 3/4HP . . . you're probably running around 60 GPM, or nearly double the never-exceed rate.

There's a LOT of back-story on this that I can't go into right now. But what I'm beginning to suspect is that blowing dead algae THROUGH a sand filter actually breaks the algae particles into even finer particles . . . and that after they've been broken, they not only cannot be filtered with sand filters, they are difficult to filter even with cartridge or DE filters.

There are two sorts of solutions here: preventative and curative.

+ To prevent this problem in the future, we need to make sure flow through your system NEVER exceeds 35 GPM, except when you are backwashing, and that it never exceeds 45 GPM even then.

+ But, to cure the problem, we've got to find a way to get the algae out BESIDES filtering . . . because if I'm right about all this . . . you can't filter it, now that the high rate flow through the sand has shattered the algae particles.

So, I want to try this
1. Make sure your chlorine is 20 or more this evening, and that there is NO live algae left.
2. If so, turn your pump OFF, and leave it off.
3. Check chlorine levels tomorrow PM, and make sure they are 10+ . If not, add a gallon of plain 6% household bleach.
4. Check Monday am, and see if there has been any change. Let me know what you see.

[TheGoose]

This sounds exactly like what is happening with my pool, except that I have a 1-HP pump and a 300# tagelus sand filter. Water color is good, chlorine levels are holding, all other chemistry looks good, water just won't clear.

Ben do you think turning off the filter will let the particles settle?

[PoolDoc]

Ben do you think turning off the filter will let the particles settle?

I don't know. I'm going to be recommending a 3-stage trial:

1. Try to settle with nothing. Vacuum to waste if it works.
2. Add floc, and try to settle. Again, vacuum to waste if it works.
3. Add clarifier, and try again.

During the recirculation steps (2 & 3) it will be important to bypass the filter. I do know that sand filters can 'break' floc agglomerations.

[sosspenc]

Thanks!! The pump is a Hayward SuperPump if that helps any. I just checked and adjusted the cl- to 20; it was between 15 and 20. I'm going to let it circulate for another half-hour and shut off the pump. I agree that the dead algae is going right through the filter. The first few days I was needing to backwash every few hours; now the pressure rises maybe 1-2 psi over the course of the day..even with the DE added. I will report back with results on your recommendations. Once again, thank you so much.
Stella

[PoolDoc]

Yeah. A 3/4HP Super Pump is almost certainly over-driving a Tagelus 50D, which shouldn't be run at more than 35 GPM max. If you have an up-rate Super, you're probably running 40 - 50 GPM.

Tell me what your clean filter pressure is, and I can estimate it more accurately.

[sosspenc]

Clean pressure hovers between 11 psi & 12 psi. When I restart pump, I can check that against another gauge. Thanks!