Do NOT get "pool-stored"! Chlorine lock is a pool biz marketing myth (though some pool guys actually believe it).

Buy a cheap OTO (turns yellow) drops kit. If your chlorine is high, it will turn ORANGE (ok) or maybe brown (not so ok). Order the DPD-FAS.

Carl, RH-mom => you can use DE to TEST any filter: if you add a small amount of DE (coffee can) to your skimmer (pump ON) and shortly after see cloudiness from your pool return . . . your filter has problems REGARDLESS of what type it is.

RH-mom => for your pool (~30,000 gallons) ONE WHOLE BOX of borax is a small amount. Add slowly to the skimmer, but don't add just a cup.

Next steps:
1. Get the OTO kit so you can get some idea whether your chlorine is high or low.
2. If it's low, keep dosing in the PM, till you can hold high levels overnight.
3. If it's high, and stays high overnight, just maintain "orange". (If it's "brown", add 2 quarts of Baquacil or Softswim shock -- hydrogen peroxide, 31% => GLOVES & GLASSES without fail!)
3. Use a SMALL amount of DE to TEST your filter. (If you have to get a large bag, you can use it later to 'help' your filter with the cloudiness.
4. Get the FAS-DPD kit from the Amazon link -- but get an OTO kit locally ASAP.

Ben