Chemicals for pool closing

[angelald]

We have a 90,000 litre inground pool (approx 20,000 gallons). What chemicals do we need to close the pool, and how much of each chemical?

Thanks!

Angela

[chem geek]

If you are not in a freezing climate and can keep the pump running perhaps 2 hours a day (assuming the water is cold), then you could continue to add chlorine to maintain the pool and will only need to add it infrequently since chlorine usage will drop considerably from around 1-2 ppm FC per day during the summer to perhaps that much or even less per week.

If you are in a freezing climate, then read this link which is for closing an above-ground pool, but mostly applies to in-ground pools as well. Chemically, you shock with chlorine, let the level drop to normal, then add a large dose of PolyQuat 60 algaecide keeping the pump running for 24 hours, then shut off the pump, blow out the lines (put anti-freeze in them) and plug them, etc. In addition to use of the algaecide, the key to avoiding algae is to close as late as possible so that the water is cold and then to open in the spring as early as possible before the water warms up. Even if you do get some algae, it will be easy to deal with by shocking with chlorine in the spring.

For an extreme example of clearing a pool with algae upon spring opening (that was not closed the way described above), see this link.

Richard

[Guest]

Is that your pool Richard?
Boy, what a mess!

[chem geek]

No, it's from this thread on The PoolForum, but access to that forum is limited (based on location of IP address). It's basically what happens if you let a pool go over the winter without maintaining chlorine levels or using supplemental algaecides or phosphate removers, especially if the water warms up before you start with chlorine again. I've never had an algae bloom in my pool except for a nascent one (chlorine demand rising, water turning dull to cloudy) when I used to use Trichlor pucks/tabs and after 1-1/2 seasons my CYA got to 150 ppm.