I to weekly water changes on Sunday morning, 50 gallon long using R/O water. I test before and pull out 10-15 gallons. TDS goes from 750 to mid 500s but it back to 700ish within an hour or so. I've been doing it this way for about 6 months with no issues. Fish are fine. PH, ammonia, nitrite, nitrate have all been consistant after the initial cycle.