Dead fish, bright red gills, established tank

Question
55 gal tank, established for at least 18 months.  Had about 20 community fish (tetras, raspboras, neons, mollies, zebra danios, etc.)  About a month ago we added 6-8 new fish to the tank.  All was well the first week, then many fish started hanging out at bottom of tank or in the corners, not swimming much.  All nitrites, Ph, nitrates were normal.  Fish started dying one or two at a time. No visible markings or spots at first. Fish store guy said to add salt to the water. I thought at first he said 1 tbsp per gallon - have now seen online that this is WAY too much.  Did several day's worth of water changes - 8-10 gal each time.  They continued to die and now had white spots so I treated them for Ick.  Some also had gills that were bright red, my white tetras had bright red streaks down their body and red blotches at the tails.  Started treating them with Maracyn 2 two days ago, per the package instructions.  Now the tank is extremely cloudy and it says not to change the water until the treatment is complete - 3 days from now.  Still finding 1-2 dead fish each day and remaining fish look marginal. (1) What else can I do?  (2)I'm dying to change the water, it looks terrible, although the readings are still well within the safe range - should I wait? and (3) if the fish I have left are too far gone and will die anyway, how will I know when/if it is safe to reintroduce fish into the tank?  I have the danios, one raspbora, one white tetra, and a bristlenose left.

Answer
Hi Toni;

Redness and sores indicate a bacterial infection. You are using the right medicine. It just hasn't had much time yet to do it's work.

It really is okay to make partial water changes during a Maracyn 2 course of treatment. Just do the changes right before each day's medication dose. Antibiotics added to an aquarium are decayed within 24 hours so you aren't removing anything useful. It's old and ugly and the water change boosts the fishes' immune systems too. I would also add Melafix to the tank. It helps soothe irritated skin and help heal wounds too.

If they don't feel better soon, you may be dealing with a parasite too. If it's compatible with the M2, keep using the one you used for ick just to be sure.

I hope they feel better soon.....

At Your Service;
Chris Robbins