For the sake of the tank log: the pH tested 7,5 today which is higher than expected and desired. Tapwater tested 7 as expected and is soft. Might have too much crushed coral in the filter. In another thread @TheGrissom replied “I had a look at some solubility charts of calcium carbonate. About pH 8 its stops dissolving completely but by pH 7.4 the solubility is so low it can be seen as negligible. So the pH should end up somewhere between 7 and 7.5 in reality” I removed some of the crushed coral and did a small 5-10% wc. Livestock have been doing great though, despite being softwater fish.