Is my fish tank overcrowded?

Overstocked.

It could hold 1 school of tetras and 4 guppies and 1 apple snail FULLY STOCKED

You could do a school of 8 tetras and 6 corys and no snail FULLY STOCKED

I do not reccomend apple snails. They'll overrun the tank, get to the size of an apple, and poop more then they clean. 1 will be fine but be warned when they get very large.

Well, if you work by the rule of thumb for keeping fish then 26 gallons will hold probably 65cm of fish....

then again you have to take into account the shape and etc.

Let's put it this way, I have a 20L tank and I have about seventeen little guppies. They have heaps of space and they are breeding like crazy. If there isn't enough space the fish will generally die, very slowly. But they sort it out themselves. If their too crowded they'll kill another fish to keep it balanced. But personally I think maybe start off with maybe twelve fish? Just a few. You can't put a whole heap of fish into a new tank. Start off small. They should breed together anyway so soon you'll have your own little family of fish.

You are not that overstocked. I have more fish in my 30 gallon. I recommend getting double filtration. So getting two 30 gallon filters and putting them on each side. Also change your water about 30% each week. I have been fish keeping for a long time. If you keep up with maintenance you won't be over-stocked. Your current stocking level is 118%, according to http://aqadvisor.com/AqAdvisor.php?AquTankName=&Aq...

My site: http://fortheloveoffish.webs.com/

My YouTube channel: http://www.youtube.com/user/Loveoffish1?feature=gu...

Add: If you haven't stocked your tank yet take-out the school of black-skirt tetras. They can fin nip and they are on the larger side of tetras. Then your stocking level would be good.

I would get a odd number of Cory cats so like 5 and I would only get one snail unless you want a tank filled with baby snails I wouldn't!

I would suggest you forget about one of the tetras and stick with one snail, not two.

Yeah, it would be way overcrowded.

hmmm.. i think so. maybe you should buy a bigger tank.