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

[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.

[SunnyOptimism]

See for example - http://poolservicestech.com/tag/reverse-osmosis/

RO is a boom-bust business. When water is cheap to replace, it can't compete. However, with recent price increases here in municipal water rates, RO is starting to come on par with water replacement. As long as the company you choose uses industrial grade equipment (not the under-the-sink garbage you get at HomeDepot), 80% recovery is very achievable. It's all dependent on the water pumps and pressure you use, the higher the pressure, the better the efficiency. Typical filter membrane pressure is anywhere from 250-300psi. Normally these companies have to back a truck up into your yard and the process can take a couple of days depending on water volume. High pressure, industrial units typically process a few thousand gallons per day. Desalination typically requires several filter units cascaded together as a single RO membrane can only fractionally change the salt level.

Yikes! A chemical that eats CYA?!? Not sure I want that in my pool

[CarlD]

Portable and even hand-pumped RO units for desalinization to make drinking water have been available for boaters/yachtsmen for well over 20 years. They are very pricey, though.

[FormerBromineUser]

Jtran, I thought you were maintaining a FC level of 25. Not?

[CarlD]

Keep that FC up, but do NOT use Di-chlor powder or Tri-Chlor tablets, and certainly not the HTH sticks. Stick to bleach or liquid chlorine. With your CYA that high, once you kill the algae, you'll be able to maintain a residual FC level easily, probably best to keep it close to 15, and won't have to add much bleach at that point.

If your CYA is really that high, you can safely bring your shock level to 30 or 35ppm without damage to your pool.