So, yesterday, for the first time since we set up our pool on July 4th, it smelled like chlorine. Odd, since the chlorine had tested within the range of normal, and I had added only enough bleach to bring it up to the high mark of the normal range. I swam anyway, but wondered... later, I realized...
Now, if I hadn't gotten myself as well-educated as I could about cheap, simple pool care, I might not have realized there was a problem. Pools are supposed to smell like chlorine, right? That's how you know they're clean!
Wrong. A well-balanced pool, I learned, near the end of last summer when it was really too late to make good progress on last year's pool, smells like nothing or smells "clean." A chlorine smell means a possible burgeoning combined chlorine problem.
This morning, I tested the pool with a simple test kit that only tests total chlorine. (It's all I have right now. Next year I'll get a more comprehensive kit) The total chlorine number had gone up overnight.
Now, that ain't right. Unless my neighbor was sneaking bleach into my pool in the middle of the night, that's quite suspicious.
It appeared that the total chlorine number was around 5ppm. (These tests aren't super precise.) So this morning at about 11 am, I used an online pool calculator and information about proper shock levels to raise the chlorine levels to around 12ppm. (Again, some guesswork needed because I don't have a kit that tests chlorine levels above 5ppm, although you can get a rough idea.) It was about two cups of 8.25% bleach.
By 5 pm, the chlorine smell was gone. A test with my little OTO style test kit at 7:30pm showed chlorine in the "very dark yellow" stage (see the "rough idea" link just above), so between 5-15ppm. Much higher than you'd want to swim in.. but with zero chlorine smell.
Isn't that crazy? Raise the chlorine to get rid of the chlorine smell! It's like magic!
Now I will test the water first thing in the morning before the sun hits the pool and starts burning off chlorine, and if I've only lost a little (i.e. no change in the color; I can't test precisely) I'm going to assume I've nipped combined chlorine in the bud and simply keep a close watch on things. If the color changes a lot and has dropped down into the range where my test kit registers, I'll know that there's still too much organic matter decomposing and turning my good chlorine into bad chlorine.
Now, that's all not very precise and it would be much better if I had a fancier test kit, but it's the best I can do for now. I figured it's probably better to get the chlorine a little too high and have to wait more days to swim than to let the pool sit cooking combined chlorine and end up having to close down the pool sooner than I want to because it's just gotten gross!
PS: So now you know. When you walk into a public pool area or a hotel pool and there's that strong smell of chlorine, that doesn't mean the pool is clean. It means it's dirty enough that the sweat, urea, and organic matter is "eating up" the chlorine and turning it into other compounds that smell like chlorine but don't sanitize like chlorine... Ew, ew, ew.