carbonate hardness <kh> and phosphate <po4>

[tgoeujon]

how hard is too hard? my top up water is usually at 140 mg/l but for some reason my tank is sitting at 195 mg/l. all thats in it is 2 seahorses and two pipefish with a clean up crew. my phosphate which is usually at nothing has spiked at 5 mg/l. i know i need to do a big water change but will altering the kh and po4 that much hurt the fish. also will the water being that hard actually hurt the fish or cause a reaction of some sort.