Christopher Lewis wrote:
My girlfriend bought me a 100 litre tank for my birthday a few weeks ago. I
filled it with gravel a few fake plants and water and left the filter and
heater running for a few days.

I then went to my local fish shop and bought some small fish recommended by
them to cycle the tank.

All OK so far right.

So far, so good.

Then.... My mother boyfriend turns up at my house after 2 days of the fish
being in the tank with a bag with about another 15 fish in it. They are
gourami's, 2 or three different kinds of mollies, a few red eyed tetra's (i
think thats what they are called), some tiger barbs, some sharks someting or
others (cant remember and i doubt they are real sharks).

Oh my. 15 fish?!? I've gotten gifts like that. The sharks are not
real sharks. A lot of fish go by "shark" and none are suitable for
your tank. Red-tailed and rainbow sharks - relatively small,
aggressive cyprinids. Bala sharks, endangered, large, and skittish.
Irridescent sharks, which get huge.

So now i am doing a 20% water change every 2 days in an attempt to keep the
ammonia and nitrite levels down. Yesterday ammoina was somewhere between 1
and 1.5 ppm so i did a 40% water change.

Nitrite is about 1.0 ppm at the moment. they have all been in there 2 weeks
now and *seem* OK so far.

Is there anything else i should be doing?

Water changes are good. Add 1 tsp/gallon of salt to help counteract
the effects of nitrite poisoning. When you change water, only add the
salt to the replacement water.

Seed bacteria. Get Bio-spira, or gravel, plants or filter media from
an established tank.

Good luck. Unfortunately, you'll need it.