Pleco died, new to hobby please help!

[RoxaStitchXIII]

I am new to the hobby and I have done a lot of research on keeping fish but I just can't figure out why my little pleco died(he was on the top of the tank when I woke up this morning). His belly wasn't sunken in and I saw him eating last night after I turned the tank light off, he was quite active and has been since I got him (3 days ago)
My tank is 6ft tall and about 2ft across and 2ft deep and an octagon shape(I don't know what that is in gallons)
I tested the water for everything before I put them in and even got it tested at my local fish shop, and they said the water was pefect, the tank had been cycling for around 6 weeks before I put any fish in it and there was already some algae building up, but I also bought some plec pellets for it to be sure it was getting enough food.
He was only a small pleco and I have 5 other small fish in the tank, 2 small sucking loach, 2 small Kuhli loach(who hide until nighttime when they go crazy) and a small red tailed shark, the rest are all doing great so I can't understand why the pleco died.

One thing I have noticed is that one of the sucking loaches is getting slightly aggressive and chasing around the shark and other loach, but he is a lot smaller then the pleco so don't think he would have just killed him. If anyone has any idea what could have happened, maybe these fish just don't live well together or it could be something else in my environment, I just don't want to put any more fish in the tank until I know it's safe.

Sorry for my rambling, thank you for reading, Kate.

 

[eaglesaquarium]

Hi Kate. Welcome to the forum.


I am sorry to be the one to have to say this, but there's a fairly significant problem with your tank, and unfortunately, there's not a whole lot you can do about it.

The tank's dimensions are the biggest problem. These tanks are great for looking at, but they are really unsuitable for most fish. Fish swim horizontally, not vertically. So, the sad truth is that while your tank has a great amount of space in it... it is really not much different from a 2 foot by 2 foot (octagonal) footprint with only 1 foot of height. (I approximated your tank's footprint and you are looking at about 23 gallons of water per foot of height.) But... the reality is that that is the amount of space that you really should be thinking for this tank. Its just not reasonable to stock it like its a 135+ gallon tank (which it likely is... based on the height!). The surface area available will limit the amount of oxygen available in the tank.

The pleco may have actually died from asphyxiation (lack of oxygen). The lowest portion of the water might not have sufficient oxygen to support the fish that are there. It seems that you have no circulation to the lowest portion of the tank (I can't tell if there's a tube for the filter drawing water from the bottom area of the tank or not). If there's not, that would be an easy way to increase your oxygen in the tank. Also, pushing the heater as low as possible into the tank will also help with some sort of water circulation. An air stone, placed as low as possible (where it actually will work... the air pressure from the pump just isn't enough to push the air through the stone at the bottom of the tank)...

The filter intake being at the bottom is the best way to circulate the water around.


On top of this, we need to establish if the tank has been cycled (and bacteria are converting ammonia to nitrite and nitrite to nitrate...) and then we can discuss the stocking that you have and should have in a tank like that. The biggest key is to keep fish that will occupy all levels of the tank, and that swim all over... but don't need a 'big' tank. Its a challenging tank to keep due to its unique design.

 

[RoxaStitchXIII]

Thank you for replying, I have an external filter that does go quite low in the tank(about a foot off the bottom) which is where I was advised to put it, and I have a few air bricks around the tank for some more oxygen, my tank has cycled and it was cycling for around 6 weeks, I was working closely with my local tropical fish shop and they were checking my water for me said that my nitrates and nitrites were at 0 and there was no ammonia.
I've been back to see them today and they said it could be the sucking loach, the guy who sold it to me wasn't the usual one I speak to and he said they would be fine but the guy today said that it's probably that that's killed him, which is annoying because I can't put anything else in until I get these sucking loach out and take them back to the shop, which is difficult because the tank is bigger then me

I've been advised angel fish because they like to swim up and down, some small albino catfish because they stay small and go up and down the tank, and gourmani red robins(or honeys) would you recommend any of these?

Sorry I've just realised you can't see the pump because of the dodgy shape of the tank, but I promise it is there(that's what the bucket shaped thing at the side of the tank on the floor is), and I hadn't turned the light or air bricks on when I took the picture this morning which is why you can't see them

 

[Baker]

Have you kept a close eye on the temp of the water at night? Does that radiator next to the tank run at specific hours? It could be over hearing your tank but I feel like you would have already known that if that were the case.

Unfortunately beyond that it's hard to advise you on what to do because in reality that tank isn't really healthy for most fish, although in my opinion it would be a beautiful under water garden with maybe shrimp and some small schoolers such as neons or white clouds.

 

[eaglesaquarium]

What is your water parameters? pH, kH, and gH?


How did you cycle the tank? An unplanted cycled tank won't show zero nitrates. It's just not possible.