Shrinking pectoral fins on betta

Question
Hi Chris, you've been helpful before with my questions, so I'm asking again...hopefully you can help. I have a 2 gallon aquarium (charcoal filter I think) for one beta.  I do a full water change about every month or so (usually because of a buildup of algae).  I've had my fish since x-mas, but have had betas before(3yrs).  When I change the water, I put water conditioner and algae control in the tank before I put the fish back in.  I also have test strips to test for Nitrate, Nitrite, Hardness, Total Alkalinity, and pH of the water.  I changed the tank water last friday(4/17), and when I tested the water, the nitrate and nitrite came back safe, the hardness was in the middle(soft), the alkalinity was ideal and pH was neutral.  When I put my fish back in he was acting a bit strange, and seemed a little agitated.  He hasn't been very active (sitting at the bottom of his tank or right at the top next to the filter) for the last couple days, which is very unusual for him.  I thought maybe I screwed up the water and couldn't tell, so today I was trying to take some water out of the tank and put in clean water that I let sit for 30 mins and added no algae control or water conditioner (in case I added too much to the tank without knowing).  He started to swim a bit more when I was doing that, and I noticed that his pectoral fins are really strange looking.  They used to be somewhat translucent and broad, and now they are dark in color and come to a point instead of having a rounded edge!  Did I cause permanent damage?!  He can still swim, but it seems to be a bit of trouble.  Please help!  :( I feel horrible and just want him to be active again  Thanks soooo much Chris
-Ellen

Answer
Hi Ellen;

It sounds like shock. A complete water change after three weeks can be very stressful to your fish. The water chemistry changes over that time so the new water can feel quite different to him even if test results are similar. It's stressful for him to be moved from his tank to do that too. It's best to leave him in his home and make a 25% partial water change once a week instead of a whole change out less often. You can vacuum the gravel to remove waste at the same time. Weekly changes keep the water chemistry more consistent and much more comfortable for him.

If there is still a lot of algae there might be another solution for that too. Reducing the daylight hours, keeping the tank out of the sun, and feeding less food (acts as fertilizer) are two very important steps to take.

Also be sure that his new water is the same temperature as his old water. As I said before, it's best to do partial changes and leave your fish in the tank. When your fish has been sitting out in a container waiting for you to clean his tank, the water temperature in his holding container can change. Even slight variation in temperature can cause problems when a fish is re-introduced to it's environment. Acclimate him slowly to the new water as if you were bringing him home from the fish store for the first time. Float him in the cleaned tank in a baggie of a little of the old water and let it float there for ten minutes or so. It prevents temperature shock. Make sure you leave a big air bubble in the bag so he can breathe. If he seems to be having trouble swimming he may have experienced temperature shock. Just wait it out with him and keep things as quiet as you can. Hopefully he will recover just fine on his own.

Betta fins can change color and clamp up when they are stressed so hopefully was he recovers they will return to normal. I hope he feels better very soon...

At Your Service;
Chris Robbins