Strange Problems....

[Shroomazon]

Hi,

I've had the same tank for a number of years now, it's only a small one (about 22litres I think).
I've only usually had Neons and a few loaches in it.
After having a few years some of the fish have died etc, and it was looking a bit worse for wear so I decided I'd sort it out and make it look more appealing, so I bought some guppies, a few neons and some plants to give them somewhere nice to hide in.
So as it stood, I had 4 neons, 5 guppies, and a plec (which has grown quite large I might add). +2 medium sized plants.

It was going fine for about 2 weeks, and I started to notice the numbers of the fish were dropping.
Next thing I know, I'm down to 1 guppy, 2 neons, and the plec is still at large.
Not a body to be found, so I can only assume the plec is consuming the bodies after they've died, as it's a municipal fish, so I can't even see the bodies to try and diagnose what is happening.
What is also strange is that I've noticed a baby guppy sprout literally out of nowhere. It's surviving quite well too! (I supposedly purchased all male guppies)

I came home from work yesterday, to see the remaining adult guppy has bent into almost an L shape, and I can't think of any reason for this. It's also read at the bottom, which I can only assume to be it's innards not being in good shape...
I can only come to the conclusion that it has become stuck/had something fall on it, although nothing in the tank has moved so I really have no idea what has happened.
It can't be nice for it, and I want to put it out of it's misery as I'm sure there's nothing that can be done for it, however I want to do it in the most humane way possibly, or I'll have an extremely guilty conscience!

tl;dr:
How come my fish are dying/vanishing?
What can I do to prevent it?
How can I increase the chances for my baby guppy?
What should I do about the plec? I think it's getting oversized for the tank, and I'm sure it's the troublemaker at large.

Any advice here is appreciated, I'm really at the end of my wits trying to figure what I'm doing wrong, as it's been fine for years!
Thanks in advance

 

[CheniseMummy]

22 litres is very small, really not big enough to keep those fish at all. Fish in cycling with build of of poisons have killed your fish.

Edit to say.

Buy bigger tank or reconsider fish and stocking levals
Do cycle your tank first or follow rules and buy a water tester.
add fish slowly and water change regulary

 

[swanseastilo]

That tank is way to small for all your fish.

What plec do you have.

Copied of a site.

DEFICIENCY DISEASES

Except for vitamin D deficiency, very little is known about fish deficiency diseases. The very nature of their natural food almost warrants they receive all the known vitamins, but under artificial conditions they could conceivably have a deficiency. Mineral deficiencies are doubtless common, a fact we can determine knowing the inadequate diets often fed to guppies.

Rickets
A disease caused by a deficiency of calcium or phosphorus or vitamin D; one, two or all three. A crooked spine and the resulting bend in the fish's body is the usual evidence, although the unfortunate humpback can live and even reproduce. It is not a pleasant sight among the fishes of the aquarium.
Proper lighting can prevent D deficiency; the active rays affect ergosterol in the skin of the fish and change it to the irradiated form which is vitamin D. Sometimes whole aquariums will show bent spines but generally only a few of the fishes are affected. There is no treatment; it is all a matter of prevention which is primarily a matter of proper feeding of a complete diet. TOP

 

[fluttermoth]

It could be that as the plec has grown, he's gradually overwhelemed the filter to a point whwre it can no longer cope with the fish's wastes.

 

[Shroomazon]

As far as I know it's just a pleco. It looks the spitting image of this though:
http/en.m.wikipedia.org/wiki/Filelecostomus_700.jpg
When I got it, it was a tiny thing. Now it's a good 4/5inches.

What I'll do for now is test the water levels on Friday, and from there see what I shall do next.

What's the maximum amount of fish i should be looking at for this tank?
I have been looking at upgrading in size, although had to put it off due to being to skint at the moment!

Again, thanks for the help.