I have had bettas my entire life, always in pretty small bowls (I didn't know what I know now). I currently have two bettas, Scully, who is pretty ill right now, and Krycek, the newbie. Scully is in a brand new 5gal tank, with a heater, filter, thermometer, and a few plants. I'm hoping he will make a full recovery - he has a nasty case of fin/body rot. Krycek is in Scully's old tank, a 1.8-2gal with an under-gravel filter, a plant, leaf hammock, and a super tiny heater that is keeping the tank at 80F. I probably shouldn't have gotten a second betta, when my first is so ill, but I saw him at Petsmart and just fell in love.
Here's my question - because Krycek is in such a small tank, I know I need to do frequent water changes. I have been doing 25-50% with a gravel vacuum two to three times a week, but I am wondering if I should be doing a 100% change too? I'm not really sure how the undergravel filter really works, theoretically if the gravel is vacuumed well, then it will work and keep the tank clean, but because it is so small I'm not sure if this is sufficient. I was thinking about dividing my 5gal once Scully is feeling better, but for now Krycek has to be in the smaller tank and I want him to be happy. So far, he seems to be doing well but I just want to make sure he doesn't get sick! Scully was sick when I got him, I think, and I didn't keep up on cleaning his tank (he got a 100% water change every couple weeks when the tank got really green, didn't have a gravel vac at the time, I wasn't a very good betta owner
) and so he just got worse and worse before I even realized what was happening (I thought he was just getting old). I feel terrible and don't want to make the same mistake again. Advice would be greatly appreciated!