Salinity level

at would cause the salinity levels to jump from 1.026 to 1.030 I'm using a ATC refectometer.
Tank is a 56gl column, running a Eshopps RS-100 sump, Eshopps overflow box PF800, skimmer Eshopps S-120, powerhead Rossmont Mover M1200
Water tests as follows:
PH = 8.2 Red sea test
KH = 9.3 Alk = 3.30 Salifert test
NO2 = 0 Red sea
No3 = 0 red sea
NH3 = 0 red sea
PO4 = 0 red sea
Ca = 450 salifert
Mag = 1500 Nyos test
Fish load:
2 chromis
2 firefish
1 reef safe flasher wrasse
1 stary blenny
about a dozen snails (I know not enough for CUC)
1 emerald crab
top off is just RO/DI WATER
Thanks for any and all in put