Regarding red sea calcium: the component B mixed with C, loses color over a couple weeks. I added component "B" again to titrant "C" and that did the trick. I am am reading 470 which makes sense However I will eventually run out of component B.. I contacted red sea in the hope they can sell provide more of the component B indicator so I don't have to keep buying new kits. Its important to use the smaller 20 ml bottles since every couple weeks need to add more B indicator powderI have similar problem, tried a bunch of test kits with differant issues:
Red sea MG working decently vs red sea manual test,
red sea calcium at first agreed with manual test 500 ppm but low results after a week or 2, ie 300 vs 500 w/ manual test
api nitrate at first got 3 ppm which compared favorably with salífert manual test but this degenerated to 0 ppm over a couple weeks vs 7 ppm salífert manual test
Alkalinity I have 2 tests. Red sea and salífert.. Salífert initially made sense then degenerated red sea gave me a lower result vs salífert manual ie 5.9 vs 8.3 dkh. I tested my water at 90% concentration and got a corresponding reduction in red sea to 5.3 so maybe just need a correction factor, it would not read at lower concentrations ie 75%
I will try other kits.