Thanks a lot for your help,
My tank is quite new, about a month and I got the 2 clown fish last week. One of them started to get lazy and stayed on the ground, a bi ton the side. But then looked better and suddenly down again. Today I saw him close to the filter and I thought that he was dead

but when I opened my aquarium I still saw him moving. I tried to give him food but he didn't eat anything. and now couple of h later it seems ok again. I really do not understand this behaviour and what I should do. My clown fish is still in the tank since I do not have an appropriate QT running.
In my tank, i just have these 2 clown fish, 2 cleaner shrimps, hermits and snails. One violet algae that I am not sure about the name (maybe chondrus crispus) and a briareum neon.
The parameter from the water looks fine but I just have few of them. Nitrate and nitrite are close to 0. GH 16°d. KH between 3°d-6°d. Maybe the pH is a bit low around 6.6. Cl2 0. For the salinity I use also an hydrometer and salinity is at 1.023.
It seems also that he starts moving when I coming close to the aquarium. Here the pictures that I did now. But I do not see any particular symptom...
I didn't treated them with anything yet since I do not know what can be the problem

and I didn't observe a weird breathing
I hope you will be able to help me... Let me know if I could give you more information