Debris in fish tank.

Question
Hey Chris,
I have a 10 gallon tank that has been set up for just over a month. I have lost 2 out of first 3 fish purchases, but right now have maintained, so far, a black fin shark, male beta, and 2 Danio's. I do not know the pH, ammonia and nitrite levels. I did not know until yesterday that I should of had my water tested. Majorly misinformed in the beginning. Anyway now I have some brown junk on the white gravel. What is going on here? Is this too much food and now it is rotting? which I suspect after reading up on it today. Will a gravel vacuum removed this or do I need to do something else. I have removed almost 25% of water and replaced with treated water today.
Also, sorry for a lengthy letter, but I was told these fish would be fine with no thermostat and now I read that most need regulated temps. HELP! I have a feeling that is one of the reason my mollie and swordtail died, water temp. I am reading now that I should not have started with a 10 gallon tank but should have been at least a 20. Should I go ahead and upgrade.
Thanks Chris,

Cheryl

Answer
Hi Cheryl;

Oh, that's too bad you have been so misinformed. It happens far too often I'm afraid. They do need a heater, but I think what killed your others is "New Tank Syndrome". Here is my article about it;

http://www.xanga.com/Expert_Fish_Help

The brown junk is probably just algae. Vacuuming the gravel will help. It is a type common in newer tanks. If it is fuzzy looking or like carpet or cotton, it is decaying food. The remedy is the same....vacuuming as well as cutting back on feeding. Replace 25% of the water every week and vacuum the gravel every 2 to 4 weeks.

You have another looming problem as well. The blackfin shark will eat those other fish as he grows. He gets pretty large at over a foot long. (yikes!) Here are profiles on all your fish;

http://www.fishprofiles.com/files/profiles/328.htm
http://www.fishprofiles.com/files/profiles/545.htm
http://www.fishprofiles.com/files/profiles/484.htm

I hope everything turns out okay.....

At Your Service;
Chris Robbins