Black or dark green algea

Question
The bottom of my tank is a compleat carpet of black algae or else it is just really really dark green and it is very slimy I cannot stand it!!! My husband and I have done water changes changed out all the rocks and my tank is beautiful for about a week and the stuff comes right back and no one can tell me what it is and how to get rid of it the water in the tank is crystal clear except for the carpet of algae and it also turns any plants or figures I have in the tank black also. WHAT IS THIS PLEAS HELP!!!! my tank is a 55gal. I have had some fish die due to this problem pleas help.  THANK YOU

Answer
Hi Barbara,

The 'Algae' that you are referring to is not true algae. The black slimy algae, with a slight musty odor that starts to grow and covers everything is actually a type of bacteria.

It is caused by poor water quality and excess fish waste, two things that result from lack of proper aquarium maintenance.

As a general maintenance routine, a 20% water change should be performed every week, with a through cleaning of the gravel via a gravel vacuum (a siphon with a tube that sucks out waste from the gravel, without removing the gravel from the water). If you do not have a gravel vacuum, buy one from your local fish store (they cost about $8). Following this regular 20% weekly water change/cleaning schedule will prevent any future bacteria.

Since it's already present in your tank, the best way to completely eradicate it would be to first, manually remove it as you've been doing, and then dose with a half-dosage of an antibacterial aquarium medication for one week. I'd recommend Mardel Lab's Maracyn. This should kill off all the bacteria, and it will not grow further if you have a regular schedule of water changes.

Good Luck, and Happy Fishkeeping!