Toping off with RO/DI, even one that isn't working great, should be keeping your TDS down. Folks that top off with declorinated tap water can get a HUGE TDS buildup over time. It is probably just high Ca (450-500) and your test kit isn't acurate at that level. Try testing with 1/2 Salt 1/2 RO/DI and see how your test kit does with that?Originally Posted by cvonseggern
When you can, pick up a Salifert Test Kit - I saw they had some under the counter at Alamo Aquatics yesterday!



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