Closing a pool? What on earth is that????
The water chemistry stuff is probably the most fun, maybe I can add a quick tutorial for the most important stuff. Cleaning and maintenance not so much. I've met so many people who've had a pool for years without really understanding any of this, so it can be done. But it's not all that difficult and you'll be able to preempt problems if you can stay on top of a few basic things.
- Chlorine
This is probably the most important aspect. You'll have a green-scummy pond in no time if you don't stay on top of it, especially in the heat of summer when we are constantly filling the pool with sweaty people and animals.
By 'chlorine' (in swimming and potable water) we are actually referring to hypochlorite (OCl-) and hypochlorous acid (HOCl). The proportion of each is determined by the pH, which we'll get to in a moment. With test kits you will likely see the terms "Free", "Combined", and "Total" when testing your pool. Quite simply, Free + Combined = Total.
Free chlorine is hypochlorous acid and hypochlorite that are 'free' to do work - sanitize!
Combined Once this free chlorine is 'used', or combined with ammonia in our sweat (and yes, urine), it is considered 'combined' as a chloramine/dichloramine/trichloramine. These are very poor sanitizers and are responsible for the classic swimming-pool-chlorine smell.
Total is the sum of free + combined, or 'available' and 'used'.
The goal is to keep a small amount of free chlorine for sanitizing (without too much or too little) while minimizing combined chlorine. I believe 2-4 ppm is a good target, although you can go lower if you pay close attention. Get a test kit that will let you see 2 of the 3 (since you can just calculate the 3rd). Otherwise you're just flying blind. You need to know free AND combined.
- Shock
What do we do when combined chlorine starts to climb? As free chlorine does it's job, combined chlorine will rise. I try to keep combined chlorine under 1-2 ppm, and certainly well under my free chlorine. To do this, we add a large dose of chlorine to oxidize the chloramine. (So you CAN fight fire with fire!!) There are several types of chlorine and non-chlorine shock that can be used for different circumstances. It would be wise to familiarize yourself with them and why you might choose one over another. I personally prefer liquid chlorine since it doesn't raise calcium or cyanuric acid levels. Whichever you choose, it should be repeated until a stable free chlorine level can be achieved. If you shock regularly, this won't be something you worry about.
- pH
Above we discussed that chlorine sanitizer exists in 2 forms in the pool: hypochlorite and hypochlorous acid. Hypochlorite is not a great sanitizer, but is stable. (Bleach!) Hypochlorous acid is a much stronger oxidizer so we target pool pH to keep it over 50% in equilibrium with hypochlorite.
At around pH 7.5, roughly half off the free available chlorine will be hypochlorous acid. When I see pH reach 7.5, I add muriatic (hydrochloric) acid to lower the pH to about 7.1. Maintaining the pH in this range will ensure that 50-75% of chlorine will be hypochlorous acid, some serious disinfecting muscle! Remember, the free chlorine test only tells us the total population, pH will determine which form it will exist.
Also of note (but hopefully not so much in your pool!) as pH drops below 3, chlorine will exist as a 3rd species, chlorine gas! Obviously this can be very dangerous and the reason we don't mix acid and bleach. So... yeah. Don't add a truckload of acid to your pool.
Alkalinity
As with brewing water, alkalinity is the measure of the buffering capacity of the water, or how easily the pH can be changed. With most 'normal' city and well water used to fill a pool, alkalinity tends to normalize itself with proper attention to chlorine and pH. Too low and the water can etch plaster and you pH may bounce around more than you'd like. Too high and you may get calcium buildup on heaters and have a tough time getting pH to come down. 100-300 is often cited as a good general target, although you could probably fudge that a little. If you are anywhere in that range and not having problems adjusting chlorine and pH, you are fine.
- Stabilizer (Cyanuric Acid)
When struck by UV radiation from the sun, both hypochlorite and hypochlorous acid undergo photolysis. Translation: we lose our sanitizer in the sun! Stabilizer is used in pools that are exposed to the sun's UV rays in order to protect the chlorine. It is quite effective however it does reduce the sanitizing ability of the chlorine. Too much and the chlorine has a difficult time oxidizing the nasties all together.
30-50 ppm is plenty for almost any pool, although there are people here in Hades that use more. (We have, uh, a little sun here) What most people might not realize is that many chlorine tabs (the little white hockey pucks you put in the floater) already contain cyanuric acid. If left unchecked the levels will eventually get out of control. You'll be left with ineffective chlorine and end up doing a partial drain/fill to dilute the water. (Trust me, this would still be cheaper than the cyanuric acid reducing chemicals) If you test and see you're getting north of 50 ppm, stop using stabilized tabs. Read the bucket or ask the sales clerk for help finding non-stabilized tablets.
There are plenty of other products on the shelves at the pool store (i.e. clarifiers, algecides, etc) but if you keep the basics in line, you won't need them very often.
Enjoy the pool. It always feels like a giant sweaty liability while you're working on it, but there's nothing like a homebrew in your own pool.
Mmmmm..... homebrew