first sw tank

Hi name is middy live in UK had fw for years so finally done first sw 75gallon tank
Filter fx6 very well maintained
2x165 watt leds
2 jecob w4s
2 jecob w8s
2 tmc 200 watt heaters
Tmc auto top up
Twin brs reactor
22 kilo marco
15 kilo live java
55lb 1mm coral sand
Bubble magus e5 skimmer
Tank is two months old
Ph 8.1
Salinity .25
Temp 78/79
Ammonia 0
Nitrite 0
Nitrate 15
Phosphate 0
Cal 420
Mag 1320
Alk 10.5
Opinions on readings off tests would be good please bit worried about nitrate
10% water change every 10 days
5 stage ro di unit tds in 266 tds out 0