I can't tell if the edges are dark or not, that's usually the best indicator of fin rot. Frequent water changes, daily is best, to help stave off fin rot. Depening on what size bowl you have, you may just be able to do daily water changes, just remember to keep the water close to the same temp, and use dechlorinator.
You could use API stress coat instead of the dechlorinator, it can help promote fin growth. I use it hen my boy chews his tail.
AQ salt is another option, 1 tsp per gallon is the dosage. With salt treatment daily water changes are needed to keep the salt from building up.