slow - zero coral growth

[saltyrockbox]

75g tank bioload 3 small clowns, small 6 line, small foxfaced rabbit fish, I feed a 1/2 cube of frozen whatever I have or a pinch of flake every day, lots of zebra and blue hermits one starfish and one coralbanded shrimp,
I tested nutrients for a long time and for about 3-4 months was getting zero, I have been dosing Ca & dKH by hand after testing a couple times a week I have auto top off and with the new lights and fans go through A LOT of fresh RO water. My RO system is crapy nano systme i got a while back I have not tested its performance, maybe I should do that.