Just bought a house with an inground vinyl pool, approx 33,000 gallons, previous owner used chlorine tablets, water looks clear. Found this sight, started reading, ordered the TF-100, and results are:
FC: 10
CC: .5
TC: 10.5
pH: below the lowest color, so <6.8
CH: 300
CYA: 95
1) So my 4 kids really want to swim...is the water safe?
2) The pool math calculator says to replace 58% of the water to get the CYA down. Will CYA come down on its own over time, or is replacing water necessary?
3) Assuming the high FC will come down over time if I'm not adding more chlorine...is that correct?
4) pH seems off, but maybe due to high FC?
Thanks for any help!
Welcome!
A steady diet of pucks will drive pH waaaaay down and drive CYA waaaay up, which seems to be the case here. What is the TA reading? You'll need to know that to calculate the dose to fix the pH.
1) The FC/CYA ratio is good. If the water is clear enough to see the bottom, after the pH gets fixed, let 'em in.
2) CYA will only come down via splashout, backwash, or draining. 95 is too high. I'd suggest you work it down slowly over a few weeks, draining maybe 4 or 6 inches at a time. I use pool water on the lawn. Just maintain the FC for whatever CYA level you end up with and things will be fine.
3) You want the high FC with your high CYA. Minimum FC should be 7. Keep it between 7 and 10 while the CYA is where it is. 7 is the minimum, 10 is the max before the pH test gets weird. It's buffered by the CYA. There's actually less bleaching power than is allowed in drinking water which is unstabilized. I took over a pool with 240 CYA and we swam at 20 FC with no ill effects. I wouldn't recommend trying it, because it's a PITA. I only did it because we were under water restrictions. It's much much easier to maintain at lower CYA levels.
4) Your pH is low because of the trichlor pucks they used to feed it. Shock powders are also acidic. High FC will mess up pH readings by making them read falsely high, not low. I'd believe that reading, and it's good that you realize it might be even lower since that's the end of the scale.
Do you have any leftover chemicals laying around from the previous owner? You need Soda Ash or pH Up - same stuff - and possibly alkalinity increaser, which is just overpriced baking soda. If not, what to buy and how to add it is
here and how to use poolmath to figure quantities is
here.