Fish are definitely an ammonia source
How many and of what sized fish do you have?
The only way to know if the tank is cycled is to test for ammonia, nitrite and nitrate. Especially in the beginning stages of fish keeping these tests are essential.
How long have the fish been in the tank?
If the fish have been in since Christmas, then the tank should be cycled
Although simply putting a handful of fish in an uncycled tank in the beginning was putting the fishs life at risk and has probably done permanent damage to them.
Algae is fairly common and could be due to a number of reasons
how often do you do water changes? By water changes I mean drain water from the tank and replace it, not just top off evaporation
Algae blooms are usually the result of an abundant food source for the algae, and algae eat waste. So high nitrates or phosphates are a common cause, but so is natural sunlight or excessive artificial sunlight. If you have waste built up then water changes will likely reduce algae growth
I hope this does not sound rude and its a common mistake/suggestion
but I suggest you find and read some articles about the basics of fish keeping. You have a nice sized tank so theres no reason not to do a little reading and make the most of it
