I've been doing BBB for a month or so now, and am happy as heck with it... Most all of my numbers have been pretty good, and I'm keeping the CL sort of reasonable (It tends to get down to 1-2 FC before I bump it back up to 4, but I'm staying nice and clear thanks to the Borax...)
However, since I started, my CH has been slowly dropping - I understand why the other numbers are changing, to the extent that they are, but I don't see why my CH has been changing... According to Pool School one lowers CH by water replacement, which I haven't been doing on purpose. We have been getting a lot of rain, and my pool has probably gotten 2-3" deeper, but isn't (far as I can tell) at the point where it would be overflowing...
However my CH has been dropping - I've been keeping a log of my numbers every time I do a test. I don't do the CH test that often as it uses a lot of reagents, and I've been told it should have been pretty stable and didn't need testing that often.
However, on 5/25 when I got started on BBB testing, I had a CH of 300. I did do some backwashing getting the opening water into shape, but by 6/09 I was done and in control, with borates and CYA where I wanted them, and a CH of 290
Today I ran the full set of tests outside in order to verify all my numbers (I'd been testing indoors at night and the "One Sheet Instruction" thread suggested that the color change tests are easier to read in daylight...) and found that everything else was what I expected, but my CH was only 260... I have a plaster pool, so I know CH is more of a concern, but that is still w/in the limits (barely) though my CSI is at -0.47, which is getting on the low side.
Any idea what would cause my CH to drop so much? Does it need anything done about it?
OTO CL 1 (approx)
pH 7.2 (I added some MA the other day, and it dropped more than I was expecting - I'm planning to just let it drift up naturally as it doesn't seem that far off)
DPD - FC 2 (Added 54 oz of 12% CL to bring it back to 4)
DPD - CC 0
DPD - TC 2
TA - 95 (has been around 100, but I'm letting it slowly drop, as ideal s/b around 80)
CH - 260
CYA - 40 or a hair under
Borates - 50, (I think, though it was very hard to tell whether it was closer to 50 or 80)
Aside from the CH dropping, everything else looks fine, so that's mostly what I'm concerned about...