Male endler sitting on bottom of tank but otherwise looks healthy

HI Guys

Yesterday started noticing one of my very cute blue endlers 'spotty' started acting a bit strangely. I noticed he was getting a bit bullied by the alpha endler and afterwards spent a lot of time at the surface of the water just sort of cruising about. Last night he started sitting around on plants/ rocks/ gravel and hiding away underneath plants - wondered if he might have been sleeping. He has exceptionally beautiful bright colours and spots, none of which have faded or show any signs of stress or damage. This morning found him still being very lethargic, he came up for feeding time and was swimming about 'normally' but then not long after went back to hiding and is currently sat in a rock cave.

Yesterday I also had to take back one of the endlers of the colony to the LFS (only had them 5 days) as it had gotten very ill, colours faded, could no longer swim properly, severely clamped fins and was just sinking / laying on its side at the bottom of the tank. Spotty is not behaving or looking anywhere near this severe - he isn't even clamping his fins - but I am worried that maybe if this is something contagious and if my whole tank is at risk.

I can get a video of him if wanted.

Tank is a 40L, fluval volcanic stratum, heavily planted, lava rock, ammonia 0, nitrite 0, nitrate 15ppm, ph 7.5, kh ~100, gh ~170, temp 25-26C
has 6 endlers, 4 blue dream shrimp, 3 snails.

Any advice would be appreciated, really love this fish and would be so sad to see him die.

edit::; another endler 'cosy' has now joined him and they're both sort of sat together on a plant not doing very much - cosy is also bright, healthy looking and no clamped fins and was literally fine this morning! Making me very worried that I somehow have super high ammonia and unable to get a reading for it or something. Have just ordered some prime to ensure anything can be detoxified. Cosy is still perking up and swimming about normally, spotty will also sort of swim about to new spots but really doesn't seem to be feeling it. Very confused! Spotty evidently isn't getting super picked on as almost all the other endlers have come to check on him and didn't do anything to bother him / when they came to check he acknowledged their presence but didn't seem to want to get away from them.

 

now solved - o2 levels had dropped

 

How did you figure that out, and what did you do to fix it?

 

How did you figure that out, and what did you do to fix it?

oxygen issue. Had new fish yesterday so lights were off all day and lots of live plants think they sucked it all up + found filter is clogged and wasn't working fully.
Thought I'd fixed it, did water change, cleaned filter, manually put in o2, spotty was swimmning around on top of the surface an hour ago fine..

Go back to check just now and find him dead upside down on the bottom of the tank. Very very upset, this was my favourite fish of the group. Feel like i've failed him, feels terrible.

 

Oh man, I'm sorry. I'm sure you did your best and gave him a good life, better than living in a store, for sure. I'm pretty new to the hobby, and have lost some guppies recently, so I know the feeling. Live and learn, eh? Best of luck with the tank, and again, sorry to hear about your fish.

 

I've only had him 5 days, and yes my first tank. I feel terrible. I thought he would make it, he was so healthy.. Such a fast decline