Hi, I have a mixed reef tank 500 litre display with a large amount of fish. I have had a canary blenny for 3 months. When I bought him he was pretty skinny, but he has gained weight over the past 3 months and seemed healthy. Just in the past couple days I noticed him laying down/ lying on rock work, which I have never seen him do before, as he is always swimming in the water column apart from when he sleeps he sticks in the corner of the glass. I thought the lying down was just him perching, but then he was hiding in a cave for hours which is something else I haven’t seen him do. Now checking on him today and he is lying on the sandbed, which I took photos of. He is kind of getting up and swimming around the tank but then goes any lies down on the sand again. His swimming also looks irregular. I haven’t seen him eat like he normally does. All my other fish and I vets look good and fine, so my parameters shouldn’t be the issue right? I added a bigger tang the other day but I haven’t seen any aggression towards the canary blenny? I have just taken him out of main tank and put him into another tank by himself with the same water as my display. Also I’m not sure if I have ever noticed this but it looks like his mouth isn’t closed all the way, is this normal for this fish? Any help is appreciated