@kizshrimp - You were right, my TDS meter was off, I broke out the calibration salt and got it dead on the money, it was about 50ppm low.
Today's readings:
Kh 6dh
Gh 10dh
TDS 192
To your point though, my TDS is still less than the combined kh and gh. Does it really work that way? Or is it possible that the two tests could be reading some of the same stuff. I used API titration style test kits. I am confident in the values assuming the reagents are accurate, they are less than 6 months old.
Also, you were spot on about the substrate, it a mixture of Rift Lake substrate and regular gravel, with large baseball size pieces of coral added in as well. My tap water is about 7.2 after 24 hours, (but 7.4 out of the tap) and my tanks buffer out around 7.4. Also spot on about the Malawis, mostly Aulonocara and other Haps, a dozen Synodontis cats, some Nerite snails, but no Mbuna, was shooting for a more peaceful tank this time. I have done a lot of Victorians in the past, I love them but they are just too aggressive for this tank.
Anyway, I changed my TDS meter to a setpoint of 250ppm to trigger the water changes. The rate of rise on the TDS is a lot slower now.
@jayc – you are certainly right. I know I am pushing the envelope here, trying to run the Africans at the lower end of their range, and the RCS and green Babaulti at the upper end of their range. I “think” I can make it work. The RCS colony is certainly thriving, lots of population growth, the babaulti isn’t yet, but then I just got them a few weeks ago. The cichlids seem plenty happy too, with frequent fry.
It is certainly working for my original goal, with was to reduce the nitrates in my big tank. My nitrates measured around 5 today, where they used to be around 40.