helloo, 2 of my 3 bettas suddenly are showing signs of fin rot. the only difference in routine for my last water change was a ph adjustment. i always test the ph of the current water, which is usually 7.0 and then test the ph of the new water, and it's usually the same. however, the last time for whatever reason, the new water was at almost 7.6 so i used 2 drops of ph down per gallon and it brought it back to neutral. 3 days later, 2 of my guys' fins aren't looking so great. one's worse than the other and i actually saw him biting his fin. can the ph down cause fin rot? my other betta looks fine, and i use the same pre-set water in all 3 tanks. i did water changes on the other 2, luckily the ph of the new water was fine so i didn't need to adjust it and threw in little bit of aquarium salt. i'm hoping the water change will help. if it isn't the ph down causing the fin rot, i have no idea why 2 of my guys got it at the exact same time :/ any suggestions?