Re: New Homeowner - Green Pool [HOLY AMMONIA BATMAN!]
UnderWaterVanya said:
I see the ammonia levels are dropping. Is that as good a sign as it seems?
Yes. When you add chlorine it combines with ammonia to form monochloramine so actual ammonia (NH
3/NH
4+) will drop (though not what ammonia test kits measure) while Combined Chlorine (CC) will rise. The chlorine also oxidizes the CC mostly to nitrogen gas and some nitrate which is why the CC doesn't go up by the full amount of FC that you add. However, the ammonia test kit actually measures the sum of ammonia and monochloramine, but CC units (ppm-Cl
2) are 5 times higher than ammonia (ppm-N) units.
So if you start off with high ammonia then if you add chlorine rather quickly then it mostly doesn't budge the ammonia number (because the ammonia kit measures both ammonia and monochloramine) but the CC number rises until it gets close to 5 times the ammonia number. At that point, more chlorine lowers both of them. In practice, it's not so clear-cut and the CC doesn't get that high so at some point both ammonia and CC start dropping. That's pretty much what we've seen in this thread with the following progression of numbers:
FC .... 1 ... 5 ..... 6 .. 2.5 . 3 . 11.5 . 10 . 14.5 . 15 . 11.5 . 12.5 . 12.5 . 10 . 8 .. 9 ... 8.5 . 7.5 . 8.5 ... 7 .. 8.5 . 11 . 7.5 . 10 . 3 . 10 . 11 . 10 . 11 . 8 . 3 . 10
NH
3 .. ? .... ? ..... ? .... ? ... ? ..... ? ..... ? ..... ? ..... ? ..... ? ....... ? ...... ? ...... ? .. ? ... ? .... ? ...... ? ..... ? .... ? ..... ? .... ? .... ? ..... ? .. ? ... ? ... ? .... ? .... ? .. ? .. ? ... ?
CC .... 3 . 11.5 . 12 . 22 .. 7 ... 3.5 . 2.5 .. 2 ..... 2 ... 2.5 ..... 3 .... 1.5 . 1.5 . 1 . 1.5 . 1.5 . 1.5 . 1.5 . 1.5 . 2.5 . 1.5 . 2 .. 1.5 . 8 .. 2 . 1.5 . 0.5 . 3 . 3 . 8 . 1.5
FC .... 8 ... 11.5 . 14.5 . 14.5 . 11.1 . 12 . 16.5 . 11 . 12 . 14 .. 2 .. 8 .... 9 ... 11 .. 5 ... 2.5 . 3.5 . 2.5 ... 2.5 .... 1 ........ 2 ....... 4 ... 4.5 ... 2
NH
3 .. ? ..... ? ....... ? ....... ? ...... ? ..... ? ..... ? ...... ? .... ? .... ? ... ? ... ? ... >8 . 4-8 . 5 .. 4-8 . 4-8 . 2-4 . 1-2 . .5-1 . .25-.5 . <.25 . .25 . .25
CC .... 4 .... 1 ....... 1.5 . 0.5 ..... 1 .... 1 .... 1 ...... 1 . 0.5 . 0.5 . 4 . 0.5 . 0.5 .. 2 ... 5 .... 2 ... 3.5 . 2.5 . 4.5 .... 5.5 ....... 2 ....... 3 ..... 2 .... 1
The varying readings between FC and CC are because of high CC bleeding through to the FC test so that if the FC test isn't done quickly enough, then it measures some of the CC. So in reality for most of the above, the CC was actually high and the FC low which is consistent with adding chlorine to ammonia to form monochloramine. When one has potentially high CC, then one should do the FC portion of the test quickly and not wait to see if the clear holds. Having the clear hold is only applicable for normal CC levels, not very high CC levels which are likely to bleed. An ammonia test kit is a secondary way to confirm since it measures ammonia and CC combined though the units are different where CC is divided by 5. So 8 ppm ammonia can mean 8 ppm ammonia and no CC or it can mean 4 ppm ammonia and 20 ppm CC or it can mean 0 ppm ammonia and 40 ppm CC. So if the FC/CC test is done correctly, then the CC shouldn't read any higher than 5 times the ammonia test reading and for the readings above that does appear to be the case.
The lessons that should be learned from this are 1) when cleaning a pool that has been "let go" where the chlorine went to zero for any time (even a couple of days) there might be bacterial conversion of CYA to ammonia, especially if the CYA is unexpectedly low and if adding lots of chlorine seems to go away very quickly within minutes, 2) when doing the FC/CC test if the clear doesn't hold for even a few seconds, then suspect high CC and confirm with an ammonia test kit (the salicylate type of test is best for this), 3) as shown from
my own experience with this, there can be more chlorine demand than indicated from the ammonia and CC because CYA may be partially broken down (especially if one catches the conversion in the middle of the process as I did so the CYA was not yet to zero). Note that in my case, there was very high and very fast chlorine demand, but the CC did not rise that much. This may be because of the intermediate partially broken down CYA products. The real tell-tale sign is VERY rapid chlorine consumption, much more rapid than even losing half the FC in an hour as could occur from sunlight with no CYA. Chlorine oxidation of algae doesn't happen that quickly either.
, post a full set of tests ... or maybe wait until tomorrow. Seems likely you will need some more CYA since your level appeared to be dropping.