Help with Corals

Hi

I have had my tank for just over 1 year and everything was fine, but over the last 2 months my corals have retracted. I do the normal maintenance things ie water change every 2 weeks, regualr water tests (also perfect). Others things have started to grow in the tank that I havent put in (urchin, snails, star fish) so I know the water is ok.

I did think it was the light so I bought a replacement but nothing happened (18w blue/white aquaone) Then I thought it was the filtration so I removed the carbon and phosterate sponge, still no change. Then I thought it was a change in outside air temp (I am in Australia and we went into winter at the same time as this problem) So I increased my water temp from about 25 to 27, still nothing. So I increased my light on hours from 9 to 10, still nothing. Its a 35L tank so only small one. I have started to add some calcium and I use filter fish food supplement too.

What is puzzling is that it used to be really good, so when people say you need better filter or stronger lights its like, well they were fine before so why would I need to change that now?

I purchased 2 small mushrooms. I have no exp with these.

They mentioned that it takes quite some time for the mushrooms to attach themsleves to a surface. He suggested that I take a small rock frag and use a loose rubber band to hold them. Has anyone ever heard of this???

Its now been 3 hours and my mushrooms turned from large and purple in the store, to tiny and dark blue. the rubber band is loose ...just enough pressure to hold them to a 4 inch rock frag. HELP