Green pool with clogged sand filter after 2 weeks out of town

[Watermom]

but the alternative for an over-stabilized pool is to run at a higher FC level which means more bleach and more frequent bleach additions which can be costly too in the long run.

Actually, pools with a higher CYA usually can get by with less frequent dosing with bleach. Some people deliberately keep their CYA on the high side for this very reason.

[SunnyOptimism]

Actually, pools with a higher CYA usually can get by with less frequent dosing with bleach. Some people deliberately keep their CYA on the high side for this very reason.

Thanks, @Watermon.

I think it all depends on what is viewed as "high" and what set point you use for FC/CYA ratio. I try to follow the 7-11 formula for FC -> min FC level is 7% of CYA with daily target FC level of 11% of CYA.

Once you get much above 100ppm CYA, the 7-11 rule becomes much harder to maintain as my understanding is FC loss rate is not constant but proportional to FC concentration. So, at a higher FC level, you tend to lose FC at a faster rate than at a lower level. That was my point about more frequent additions.

Also, shocking your pool starts to become impractical at CYA levels above 150ppm as the amount of FC needed is quite high. I wouldn't go so far as to say you'll damage anything, but it will be a significant amount of chlorine to add and maintain. At some point, you reach a breakpoint where the cost of all the bleach you'd have to add (and time spent trying to maintain it and measure it) is probably as costly as just dumping half the water and starting with a lower overall CYA.

I'm not arguing against your point as I maintained my pool for quite sometime with my CYA at 90-100ppm, but I have the luxury of an SWCG and don't have to do any jug dumping.

[FormerBromineUser]

Jtran: What's happening?

Rest: Ben, Richard, Lisa?

[jtran69]

Sunday night at 11 p.m..
fc= 15, cya =190. I added 1/3 gallon of bleach.

[SunnyOptimism]

@jtran69,

I see you're in northern CA, are you able to drain and refill or are you still in water restrictions?

A CYA of 190ppm is really very high. During "normal" operation you'd need to maintain a minimum FC level of 14.2 just to keep algae at bay and your daily target level would have to be up around 20ppm somewhere just to ensure enough reserve disinfecting power. Dumping half your water and replacing would bring you back down to 95ppm CYA which would still be high but much more manageable from an FC perspective.

That's just my opinion. I had water that got up to 150ppm CYA and I gave up trying to fight that and just dumped half my water. Since then it's been a lot easier keeping my pool water balanced.

[jtran69]

We have to ration water and the yards on our street are mostly brown -- also washing your car is not allowed. I'm thinking to about fighting this hi cya til the end of the month and close the pool for the season.
I'm adding half gallon of bleach every night.

[CarlD]

Sunday night at 11 p.m..
fc= 15, cya =190. I added 1/3 gallon of bleach.

Are you still fighting algae or is your pool clear?
If it is clear, you can maintain your fc about where it is till you close. If it is not you still have to shock up to 25-30 to clear it, and should do so before you close.

The only benefit to closing with algae is over the next several months an algae infested pool will consume CYA, but you will have a huge mess to clean up, taking lots of chlorine. But if you cannot drain and refill because of water restrictions, your choices are limited to a high CYA pool, or an algae "science project".

[SunnyOptimism]

One other option, and it ain't cheap, is reverse osmosis (RO) filtration. I know there's at least one company in southern CA doing it so there might be one up in your neck of the woods.

RO will remove almost everything from your water - calcium, salt (measured by TDS), CYA, Carbonates, borates, metals, etc. I'm not sure if companies will RO with algae present or not. You typically have to let your FC drop to zero (FC destroys the RO membrane material) and they filter and rebalance the water for you. The recovery fraction for an efficient, industrial RO system is approximately 80% so you would still need to add some fill water.

Last time I looked into it here in southern AZ, it was about 2X the cost of water replacement.

[CarlD]

What little I know about RO is that it is primarily a de-salinization tool. At one time many cruise ships augmented their fresh water with RO, but could only run it at sea, not in port. Sewage and heavy metals in river run-off prevented usage.
I don't know how much has changed with the RO technology since then.

I thin I remember Ben had looked into a chemical that could clear cyanuric acid, but I forgot what it was, how successful it was, or how expensive and involved a process.