new tank problems

i recently converted my tropical tank to salt water.its been running for 7 weeks since then im having trouble keeping fish alive.so far i have had 2 ocellaris clown fish which died after 2 days,left it a week then added 2 saddleback clowns which lasted a few hours checked water parameters but havent changed at all

i have a juwel 180L tank

internal juwel filter

internal juwel skimmer 3.0

crushed coral

20kg of live rock

2x circulation pumps flow rate 1800 l/h each one



water temp 25 °C to 26 °C

salinity is within the green lines

GH- 180

KH- 240

PH 8.0

NO2- 0

NO3- 40

ammonia- 0



i have added ph buffer but never changed the ph at all. added it for 3 days then gave up with it not changing. did a 10% water change water conditions stayed the same.

hope someone can help as to what can be wrong or what i need to do to make it right