New Pool Owner - Chlorine not holding

[PoolDoc]

Just to explain a little further: contrary to what the pool industry generally believes, cyanuric acid can be bio-degraded (eaten!) by bacteria. The bacteria can then 'poop' one of three things: nitrogen gas, which causes no problems; nitrates, which causes no immediate problem, but fertilizes algae later; and ammonia, which is a huge problem, so much that you could think of it as 'negative chlorine'.

Depending on how the bacteria have gone about things, it make take nearly 1.5 ppm of chlorine to clean up the residue from each ppm of CYA that's missing from your pool. That may not sound too bad, but what it means is that if you had 70 ppm of CYA last fall (pretty common) and none now, you may have to add 100 ppm of chlorine to your pool, before you are able to maintain a residual.

Until you have done so, you will either have to (a) drain and refill your pool or (b) add dose after dose of chlorine, till the ammonia is gone.

Just a reminder: draining your pool can be very dangerous to your pool. Vinyl liners are often destroyed when inground pools are drained; if the ground is wet, concrete and especially fiberglass pools can literally float out of the ground, when drained , and so forth. You'd better be sure it's safe before your start.

Most people are left with the need to clean up their pool water as it sits.

[AnnaK]

I have a pool that ends a season with around 50 ppm CYA and starts the next season with 0 ppm. Ben, how does a pool owner know which of the three situations you described above the pool comes under: nitrogen gas, nitrates, or ammonia? If the CYA was converted to ammonia, would there be a smell?

I start each season by adding enough CYA to get to 20 ppm (calculated, since I can't measure that low), add liquid chlorine to 10 ppm, and then run the trichlor chlorinator for a while, usually until it gets hot toward the end of May. Then I switch to just LC. My starting water has always been clear despite a fair amount of organic debris that blew in over winter.

Given my personal experience, is it valid to say the CYA in my pool is NOT converted to ammonia? Or to nitrates, because I don't have a problem maintaining chlorine? That would then be the 'test' , wouldn't it, whether the pool holds chlorine at startup?

[PoolDoc]

I have a pool that ends a season with around 50 ppm CYA and starts the next season with 0 ppm. Ben, how does a pool owner know which of the three situations you described above the pool comes under: nitrogen gas, nitrates, or ammonia? If the CYA was converted to ammonia, would there be a smell?

It's possible to test for both nitrates and ammonia, but we haven't checked to see which kits are reliable. We probably need to look for some ammonia kits, maybe from the aquarium side of things.

As far as I know, a kit is the ONLY way to tell if CYA has gone to nitrates. During startup, a pool that has lost CYA over the winter should be behave pretty much the same, regardless of whether the CYA went to nitrogen gas, or nitrates.

However, the tell-tale for ammonia will be rapid conversion of added FC to CC, followed by lost of chlorine: like this:

PM: Add 10ppm FC
Later, PM: FC-5 ppm, CC-3 ppm
AM: FC 1 ppm; CC 2 ppm

(not actual results, but typical of what we're seeing)

One very IMPORTANT fact to remind people of: when they add chlorine, they are NOT wasting it. Rather, they are getting rid of the ammonia. Also, without actual ammonia testing, the only way to tell when you're done (or getting close) is that the FC:CC ratio will get larger and larger, and the loss overnight will diminish, so you might see this:

PM: Add 10ppm FC
Later, PM: FC-6 ppm, CC-1 ppm
AM: FC 4 ppm; CC 1.5 ppm

(not actual results)

[AnnaK]

Thanks a lot for the clarification.