Clown fish at the bottom of the tank

Hi guys,

I noticed that my 2 clown fish are hanging at the bottom of my tank.. and one of them just lay on a rock.. it worries me!

I've ran all the tests i have at home.. my water is clean..

amonia 0
nitrite 0
nitrate 2
pH 8.2
temperature 77

In the morning whenever I feed them.. they swim normally, they eat.. they dont seem to be sick (physically) neither are they breathing fast..

I'm just wondering if my 2 babies could just be kinda lazy ????

I don't want them to die that would be quite tragic LOL . i have them for 6 months now ... and everything else in my tank is fine, my 2 starfishes, anemones, shrooms, urchin, crab, shrimp... blablabla! And I have stuff growing in my tank.. hmm..

the only test I didnt do is the Phosphate? maybe that could be the problem? but i'm not an expert when it comes to saltwater! Beginning problems here hehehe

HELP :D