Is this sleeping habit normal?

I have a 75 gallon tank with a variety of glofish (5 danios and 2 rainbow sharks), 4 yoyo loaches, and 4 striped kuhli loaches. The water quality is good and filtration includes an fx4 and a pennplax 1000 canister that runs through a UV inline. Two air stones and a Fluval UV3 internal filter to assist with water rotation. Hopefully that info is helpful, if not I apologize...

Anyways, one of my glofish sharks seems to have found its preferred resting place, sucked up to the fx4s intake. It shows no signs of illness or anything out of the ordinary and quickly snaps to attention if I tap the glass. It swims around the tank but when it seems to rest, it sucks up to the intake and chills there motionless.

. It has me thinking, after my initial thought of dead, that maybe its just a wise fish and it has found a nice, secure place to sleep without having to worry about floating around into the other rainbow sharks corner (opposite side of tank). Is this normal? Do some fish sleep sucked up to the filter? Or is this a sign of something maybe not normal needing attention? Between this shark and the yoyo loaches that literally sleep on their sides, my tank has just became weird to me. Never know what is next, but always having a reason to think I have some dead fish.

The sleeping on their sides is normal for the loaches. Botia species (the YoYo if the true Yo Yo [three species get confused with this common name] is Botia almorhae) do this, and if you keep the light on a timer so it is consistent day to day, their circadian rhythm will enable them to anticipate the evening and come to rest.

The behaviour of the rainbow shark I cannot comment on conclusively. I will however mention that it may be due to stress. The "shark" should be kept either as one individual, or a group but this requires a long tank, as they can sometimes be quite aggressive. With just two this is certainly a possibility; even if you do not see physical aggression, the fish do communicate this back and forth via chemical signals (pheromones) and the other one may be the "alpha." Close observation over a prolonged period (you sitting absolutely motionless for 20-30 minutes) might reveal some interactive behaviours that could clue you in to this.

Byron said:

The sleeping on their sides is normal for the loaches. Botia species (the YoYo if the true Yo Yo [three species get confused with this common name] is Botia almorhae) do this, and if you keep the light on a timer so it is consistent day to day, their circadian rhythm will enable them to anticipate the evening and come to rest.

The behaviour of the rainbow shark I cannot comment on conclusively. I will however mention that it may be due to stress. The "shark" should be kept either as one individual, or a group but this requires a long tank, as they can sometimes be quite aggressive. With just two this is certainly a possibility; even if you do not see physical aggression, the fish do communicate this back and forth via chemical signals (pheromones) and the other one may be the "alpha." Close observation over a prolonged period (you sitting absolutely motionless for 20-30 minutes) might reveal some interactive behaviours that could clue you in to this.

Click to expand...

This yellow shark is definitely not the alpha, the larger blue one is for sure. Im not sure if ones a boy and the other a girl, but blue shark approx 25-30% larger. I have noticed light "awareness" enforcement. It was more aggressive in the beginning days, approx a year ago. It never got crazy or anything, some basic weird stare downs and light head pushing. The blue shark stays on the right side of the 75 g tank (4ft L x 18in w x 20in h) inside a fairly large fake coral decoration. The yellow shark stays on the opposite side and the blue one rarely swims over.

. To rule out stress, are there any other indicators to watch for? With me not knowing any better, but not seeing any obvious (to un-pro me) indicators, it really seems like the yellow shark enjoys resting up against the intake. I could only imagine, but it doesnt seem like a bad spot, could just suck up right against it, not have to worry about drifting out if my area, plus it keeps the yoyo loaches from bumping into it since the intake sits a few inches from the gravel and those yoyos can be quite crazy sometimes. Or maybe this yellow shark is a perv (jk) lol, as long as it dont get stuck I suppose its fine. Unless this is really uncommon and usually indicates other things going on, I just dont know what else to check as water levels are good etc.

The tank seems torn between the glo look and a natural look. Basically, thought fish would be a good first pet for my 5 year old daughter, instead of a guinea pig. So, got her the glo fish and a glofish 10 gal tank. Quickly remembered (I used to have a red devil 10+ years ago) the need of cycling and upkeep of water quality, plus my daughter not seeming too interested eventually ended up returning the 10 gal tank for a 75 gal and some new fish. The glo is cool to an extent, but I am working towards *hopefully* a carpeted tank with other live plants, and one of those nice bonsai trees to replace the blue shark fake coral deco.
. Ive tried mini dwarfgrass, a couple of times but I think its the yoyos that greet me with all the floating little strands I just planted floating up top and sucked against filter. I have two water wisterias, one stays planted and the other gets ripped out every night. Completely unrelated but after uploading pics, i started thinking about the impressions lol.

There is stress between the two "sharks," clearly indicated by your information in post #3. They should be separated.