Having a problem and i cant figure out whats wrong.

[Sebsantoro]

Hi guys, so i have a 20gallon IM fudion nano tank with a AI prime light set to 80%uv and all other colour between 60-75% for about 8hours a day. My uv sterilizer is always on and my heater is always set at 78. I have 2 clown fish with a anemone, a yellow tang, 2 peppermint shrimp, a trigger shrimp, a diamond goby, 2 soft corals and 3 other corals that i do not no what they are exactly. Resently my corals have not been opening up like they used to amd i do not know what is wrong. My salinity is at 1.025 exact and my tests came out good. Alkalinity= 2.28 , phosphate=0, nitrate=0 and calcium is at 450......i went to the closest fish store and clerk made me replace my rowa. I did a 20% water change avout 4 days ago and still no corals open....fish are doing great and eating well.......any advice on what i can adjust or do to help corals open up again and grow.

 

[mcgyvr]

Alkalinity is a little low should be 2.5-4 meq/l
That can cause an issue..
Stability is key to corals.. and with a small tank like that small changes can have big effects.. and having nitrates/phosphates at zero is not a good thing either.. you need some for growth,etc..

and do not use GFO/Rowa in such a small tank either.. You have no need to be running that either and it will quickly strip beneficial phosphates and corals won't be happy..

And please take the yellow tang back to the store.. It WILL die in such a small tank.. and please research before you purchase in the future and don't trust your fish store either.. They clearly are more interested in selling than helping you..