Sidways swimming

Question
Ok, I have a 20 gallon tank with a divider.  1 betta on each side.  Yup, I have a heater, gravel, plants.. a little cave.  Really nice apartments for the little guys.  One issue though, the filter.  The betta that is on the side of the tank with the filter does not seem to be thriving.  If I leave the filter on all day, by the time I get home in the evening the little guy is swiming sideways.  He also lays on the top of the water as if he were playing dead.  I know bettas sink when they die, so I know he isnt dead.  He has difficulty swimming around and swimming to the bottom.  Its just a bad sight.  When I turn the filter off, he seems to do ok. He starts to swim normally and such after a few hours.

Is this swim bladder disease?  I know I havent overfed him so I am unsure if this is still a swim bladder manifestation.  If so what is your suggestion.

Also, I purchased maracyn oxy to help a previous betta with fin rot.  And The maycyn oxy killed him.  I am positive because I tried using maracyn oxy with another sick betta and he died quickly also.  So I assumed it was the maracyn oxy. What is the best medicine for sick bettas?
Thanks, Jake

Answer
Hi Jake,

Bettas need the filter, so is the filtration able to reach his side of the glass in order to clean his water?

This can be water-condition-related.  It sounds like Swim Bladder Disorder (SBD).  SBD is caused by several things, ranging from foods to water conditions.  

I do not recommend medicating at all, and the marycyn oxy isn't necessary.  In fact, I don't recommend giving anything to a sick betta, except for marine salt in the water.

Please try this:

Change 25% of the tank water tonight.

Thursday, change out another 25% of the water.

Change all the filter media and clean the gravel.

Feed your betta a frozen pea, thawed and squished, and see if that doesn't clear out his imapaction.

Again, I recommend dosing with marine salt rather than ever dosing with antibiotics, when they aren't necessary.  That antibiotic is not necessary for this issue.

SBD may kill your fish.  In fact, it sounds like it's a pretty bad case.

Do the water changes asap.

I hope you feel free to contact me again and to post a followup if you need to.  I'm so sorry about your betta.

Happy fish-keeping.

Renee