I am a relative newbie to pool ownership, and I hope to assist those on the same road. This particular topic was added at my suggestion, so I am posting first.
I probably wouldn't have chosen to build a pool, but my pool came with my new house. Now I am delighted to have my own pool! An indoor pool is just what I would have chosen. After all, that makes the pool usable on a rainy day and during the winter. Also cuts down on the leaves and other junk (although I still got storm debris in my pool--it's not a very tight building!)
Basically, I thought an indoor pool would be easier to deal with than an outdoor pool. True in some ways, not in others!
UV radiation in sunlight breaks down free chlorine (FC) which is why you need CYA in an outdoor pool to slow down that process. FC lasts longer in an indoor pool--BUT so do the combined chlorines (CC)!! CC's can be very difficult to eradicate from an indoor pool; shocking with chlorine won't eliminate them completely. What you have to do is try to prevent them in the first place.
To prevent CC buildup, an enzyme treatment helps; there are a number of them on the market. One example is Pool Perfect by Natural Chemistry. The enzymes assist the chlorine in breaking down organic wastes which helps prevent CC formation.
Another option is the use of non-chlorine shock such as potassium monopersulfate (aka KPMS or potassium peroxymonosulfate). KPMS does NOT remove or break down CC's but it DOES assist in the breakdown of organic wastes. In order for the KPMS to work, it must be present at certain levels in the pool on a continuous basis. This means one more test to run
There are some other tricky aspects to working with KPMS. One is that the presence of chlorine interferes with the test for KPMS! Well, just use the sodium thiosulfate reagent (Cl neutralizer) before the KPMS test. The other tricky bit is that KPMS can interfere with Cl testing, giving a false high CC reading. To get around that problem, you need a deox reagent which you add to your sample before testing the chlorine.
Can you use both enzyme treatment and KPMS? As I said I'm a relative newbie. I'm not sure if that's overkill or not! Nobody's told me it's a BAD idea, so at this point I think it's okay.
Another possible option in an indoor pool is to use bromine. I don't have a great deal of knowledge about bromine, but my understanding is that it is not *quite* as effective a sanitizer as chlorine. It's not used much in outdoor pools b/c, like chlorine, it's broken down by UV radiation. Unlike chlorine, bromine can't be stabilized with CYA or an analog. It's also more expensive than chlorine.
HOWEVER, bromine does have some advantages! Combined chlorines are problematic b/c they aren't effective sanitizers; combined bromines, OTOH, ARE effective sanitizers! So you don't have to worry about those. The sanitizing efficiency of bromine is also less pH-dependent than that of chlorine. Bromine is also an excellent choice for spas/hot tubs.
I hope that more knowledgable folks will correct any errors I may have made in this post! At this point I know enough to be dangerous. . . I'm aware that there are gaps in my knowledge, so please feel free to point out my mistakes! I won't be offended.