anyone got any idea's?

My new marine tank has been set up about 2 months now, 1 month without live rock, 1 month with live rock. At the weekend I added it's first tenants..... since then the live rock has started to get a rusty coloration pattern on it. The nitrate has jumped too 0.5 and the ph has risen from a constant 8.01 to 8.06 over 2 days. The live rock was cured in the store for the last few months apparently. The only change to the tank was the 3 chromis, one of which is listless in the tank and wont eat.

its a 190 tank

20kgs of live rock
ex 700 external filter
protein skimmer
uv steriliser
hydor koriela's

all other readings are fine........

ph is now at 8.28!

Ph should be from 8.0 and 8.6 ideally 8.4 depending on what corals you have.

Are you getting good surface agitation so your waters getting oxegenated? This should help stablise PH.

Did you use RO water to begin with? What type of Marine salt are you using? If you use RO water and a good quality Salt it should buffer the PH to ideal reef parameters.

pH is fine: 8.2 to 8.4= perfect.

Nitrate is the end product of cycling. If the liverock is as well cycled as you say, the anerobic guys deep inside will take of that for you. Don't and any more stock until it has gone. How deep is your sand bed, that will help too onne its mature.

Best of luck

Seany