Last resort for goldfish

Question
Hi, I am hoping you may have a solution i have not tried. I have a 40 gallon tank with two fantail goldfish, and 5 koi. These fish have been co existing for years. I have recently moved the tank to the new apartment, without cleaning the tank or the gravel. I even brought 10 gallons of the original water on the move. the fish were introduced back into the tank and continued to be healthy for 3 weeks or so. I then introduced a small Pleco and  a chunk of deadwood, the deadwood was from the aquarium at the store, the sales guy said it leaches a little color initially and this would skip that step. The fantails started to get white spots on their fins shortly after, we had one that was floating to the top, but i think that was due to excess food and a day without food cured that up. the koi looked fine and so did the pleco, but after about a week and one 25% water change the fantails were showing long red streaks in the tail and the koi were looking a little pale. I read up and have medicated the tank for ick, but after two days the one fantail died. he may have been to fargone as his tail was pretty much gone. I have tested  the water repeatedly and the nitrates are very high today  probably due to tail rot and dead fish. I had added a nitrate/nitrite/ ammonia filter as soon as i noticed the high nitrate which was shortly before i tried medicating for ick. Today i put a new nitrate filter in and am thinking of doing another water change and possibly removing the deadwood, maybe the goldfish are too messy for the deadwood and it is the source of the high nitrate. I can send pics if need be... any help would be great thanks.

Answer
Hi Dylan:  I have not read anything in your post the suggests the fish have ICH.  ICH does not cause tail/fin rot nor does it cause blood streaks in the fins of fish.  Blood streaks are the result of septicemia which is usually a bacterial infection not a parasitical infestation.  Nitrate will not kill fish immediately... but will cause damage over the long run. Ammonia and Nitrite are the two that kill fish off pretty quickly.  It seems to me that your tank may be toxic... either from the deadwood or from a water chemistry imbalance.  I would start with water changes of about 50% Water chemistry test do not tell us everything that happens in the tank and external factors such as paint fumes can cause fish to become sick over the span of several minute or even a week.  Household cleaners, etc can have the same effect...thus the water change.  I would stop the medication and add in aquarium salt.  If the fish do not perk up after a day or so and they are still showing signs of fin rot then I would medicate with an antibiotic the lists septicemia on its label.... Also keep your eye on the pH as the deadwood will cause the pH to change...keep me posted ... dave