Wow.....I missed one water change. Went 14 days and I had two fish develop popeye. I cleaned one of the filters with the usual 50% water change, and the fish are rapidly improving. The KH reading was 14, so I guess it was just water quality. I'll be back on weekly changes, with a 75% change. I do have 11 pretty large peacocks and haps in my 75G, but I run an FX6 and Eheim 160g, so there is plenty of filtration. That was a first !!