Betta fish novice: Marlin revisited

Question
Hi Chris -

I wrote to you in January about Marlin, the betta fish my now 6 year old son received as a party favor.  I am happy to report that Marlin seems to be thriving in his 1 gallon aquarium, which, with its light, maintains the water within the range I have read is appropriate.  My current questions are about the maintenance of Marlin's tank (mostly).  I replace between a half and two-thirds of the water in it every week to ten days with tap water treated with Betta Plus.  The problem is that after five or six weeks, there is something (dark green - algae?) growing on the walls of the tank, and adhering to Marlin's castle, the Betta pebbles and the top of the filter.  Pieces of the stuff also float in the water.  When it gets to this point, I move Marlin into a bowl and clean the tank and its component parts with paper towels, rinse it with treated water, reassemble it and return Marlin to his home.  I am wondering if this growth of green stuff is normal or if I am doing something wrong.  If so, what is it I am doing wrong?  Should I replace Marlin's castle and/or the pebbles with new ones?  In the area of possibly eccentric, should Marlin have a "toy" other than the castle to avoid boredom? (I don't know how intelligent fish are, but given that Marlin swims to the surface when he sees me, the person who feeds him, I think there is some modicum of grey matter there.)  One last question: my son thinks that Marlin may be lonely and would like to get him a companion.  Can a 1 gallon tank support 2 fish and, if so, is a catfish appropriate?  Thanks so much for your help.  Lisa K. Eastwood

Answer
Hi Lisa;

I am so glad Marlin is doing so well!

Algae is a normal healthy part of keeping fish. It is a very natural thing, just doesn't look so nice. Cleaning it the way you do now is fine as long as it doesn't seem to stress him out too much. Replacing the rocks and decorations isn't really going to help much for long. Just delays the inevitable natural occurence of more of the green stuff.

The tank is really too small for a friend. You would need a 5 gallon tank with a good filter to even have a catfish or two in there with him. Bettas are fine being alone. It's how they live in their natural environment. However, they do occassionally have the thrill of meeting up with another male to fight with and show off to females. To simulate this you can hold up a small mirror to his tank. He will think it's another male and flare his fins and gills out to scare it away. I think your son might get a kick out of that too. ;-)

At Your Service;
Chris Robbins