Fins /Nitrite

Question
HI, Chris
I have a pickle of a question, first I have a barracks system for my fish, but it does have  a 29 gallon sump with a wet dry filter system, Total water in system is around 60 gallons, It has been setup for over  two years, there is 106 fish in the system, They are HM Betta fish the , ammonia is 0, but the nitrite is .25 I change water twice a week, 30 gallons at a time, give or take 5 gallons.
I have over the last year found that after 4 or 5 months a fin issue comes up, its not typical finrot, because there is no redness, the fins just shred and tear then kinda disintegrate. I did a treatment of marcyn+ thinking perhaps a gram positive bacteria, this seems to check it but not totally and I have done 10 day treatments, I have also done maracy2 for gram negative treatments, to no avail, I even went so far as to tear down and bleach the entire system and four months later it reappeared. Care to make a stab at this? I also use methylene blue in the water, and do monthly treatments for parasites. Aqua-sol, and use some water treatments, I have well water no chlorine, but it is rather hard 17,PH is 8.2 but I use RO to lower it. I also use salt at 1/2 tsp per gallon.

Answer
Hi Al;

If the nitrites are often elevated I would say it's just too crowded with fish for the surface area of filter media  that's in the wet/dry box. Even with two water changes every week there is probably too much waste going in. The chronic nitrites will eventually cause problems like finrot and fin erosion very easily. If you can reduce feeding and increase filtering area in the box by adding more media or more poprous media, it would help I'm sure.

Adding medicines (methylene blue, aquari-sol, parasite meds, etc...) on a constant basis may be causing more problems too. They can kill off some of the beneficial bacteria in the filter as well as making pathogens become immune to it's effects. When parasites, fungi and bacteria are exposed to treatments too often, they are no longer sensitive to the effects of the medicines. This means that when those medicines are needed to cure an infection, it doesn't work. Salt is okay to use but I wouldn't bother with the rest. The filter is absorbing them too so they are reduced in their effectiveness anyway. To treat sick fish, remove them to a hospital tank without a filter.

Let me know if you have more questions...

At Your Service;
Chris Robbins