Thank you very much for your suggestions, however, our water is extremely expensive here and I hoped to be able to get things under control a little less expensively than draining & refilling, if possible? Can I resolve this without draining/refilling?

We do NOT have a cartridge filter, but rather a sand filter: Intex 0.5 HP 14” Sand Filter/Pump – Model SF15110 – 1600 GPH

You said: "Don't use the acid of any kind unless the pH goes above" But you didn't give a figure. I will presume it is above PH 8??

We have a continued problem with HIGH PH and HIGH Alkalinity, so we have regularly had to use an acid to keep it balanced. For example, today's PH readings are 8.6.

As for the Catfish...I like the results of it very much, but using it is bothersome. There is no on/off switch, instead you have to turn a lid to get it to turn on and it is very difficult. It is also difficult to get that same "lid' off in order to access the port to recharge it. Putting on the filter bag is equally as difficult.
Nice concept, but not well engineered, unfortunately.

Thanks again for all that you do here!
Peggy (TheKs)