Fish Tank Question

Question
I have a 20 gallon tank in my classroom.  I am not an aquarium fan, but I inherited this one a few years ago when I changed schools.  We have several fancy tail guppies, a bunch of little snails, and three algae eaters (one albino).  The tank was so clean I was afraid that the algae eaters didn't have enough to eat (one died soon after I got it), so I got algae pellets for them.  As soon as I used the pellets, the tank clouded up and now looks dark and murky.  Did the pellets cause it?  Also, my classroom lights have been on almost constantly (the janitor forgets to turn off the lights).  There are no windows in my room.  I feed the guppies tetra flakes.  There are a lot of babies in the tank too.  Any ideas on what I should do to clear up the water?

Answer
Hi Becky

You were probably right, there probably wasn't enough food for the algae eaters.  Do you happen to know what kind they are?  I have a feeling they're probably what's called a pleco.  They should be in a larger tank, some varieties get over a foot long.  Usually one is all that's needed for a tank.
 
Now, I'm rereading your question to make sure I understand, you've had the tank set up for a few years correct?  And you just added another algae eater and it died pretty quick?

The pellets may have caused the murky water, but I doubt it.  Usually the fish go nuts over those and they're gone fairly quickly.
 
How often do you do water changes?
And are you vacuuming the gravel with a syphon when you do this?

The fish should have some "dark time" for sleeping.  Maybe when you leave, you could cover the tank with a towel?  Leave the filter areas open so gases can still exchange, but just cover up at least the 3 sides to block most of the light.  And the tetra flakes should be fine.  

Now the with all the babies....they'll make your tank overstocked, very quickly.  Because they'll just keep breeding and breeding, which will cause the water quality to go bad very quickly, killing off the fish.  Females can have a batch of fry every month....
Here's several suggestions:  send a note home with the kids asking mom and dad if they have a fish tank at home, would they like some baby guppies(not for feeders though), buy another tank and separate the males and females-but females can continue to have fry/babies for up to 6 months-even with no male in the tank, or try to find a fish store(mom and pop stores are a bit better) willing to take them-possibly they'll give you store credit but doubtful.  Especially since guppies are so easy to breed.

Let me know on those questions.  I think the problem may be related to the water changes, but I don't want to say for sure until I know how often you're doing those.  

Christy