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Please Help! Fish dying overnight. Covered in White fuzz and bright red gills.

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Please forgive the long post. I am desperate to find out why my fish are sick and how to prevent it. I have tried to figure it myself but, this isn't the fist time this happened. I don't know what to do. I don't want to see them suffer. This afternoon I noticed 3 of my Shubunkins are covered with fuzz one looks like their skin is peeling off and two have bright red gills. They did not eat last night and were hanging at the bottom of the tank.  Until today they have been healthy and active. I have had them for almost a year.

Background - I have 4 medium shubunkins, 5 baby 1 inch Shubunkins, 2 large Comets, a 6 inch koi and three 4 inch koi.   I have three 180 gallon stock tanks and a single 110. They are in my green house and have been their since October.  The sick fish are in my 100 gallon tank. They have been in this tank for over a month. They were with my two 6 inch koi in a larger tank and I moved them prevent overcrowding. I have the same feeding, water change, water testing schedule for all tanks. If ammonia rises above .25pmm I will complete a water change that day. 

Previously, I have had two events where every fish in this tank had a rapid onset of white fuzz and some had what appeared to be lesions. Every time  the exact same symptoms. The first time I had just purchased 3 small koi and 2 weeks later they all became sick suddenly. The fish were young and new so, I thought since they were all sick it most likely was and illness they already had. I changed all the filter media, cleaned the stock tank,  and after a week or so went to a koi garden store and purchased 3 more replacement koi.  About a month later the same exact thing happened. I tried Melafix and Pimafix. They never recovered and it seemed to get worse everyday. 

After scouring the internet I couldn't pin down what was happening. I went to the koi pond and garden store and asked what could cause my fish to get sick so fast and die and if there was anything I could have done to save them. I was told that it was probably and electrical charge that caused it. It made sense as the fish all became sick in the tank with that pump. I bought a new pump and thought I had taken care of the problem. Fast forward I just went down to see the fish and was horrified to see my 3 shubunkins I had raised so sick. I am desperate to find out what is happening and how I can prevent this from happening. 

The tanks are not cycled. The original tank was overcrowded and I realized I needed more space. That is why I have four tanks. It was either have them with a daily ammonia spike of 1ppm or split them up and work daily with small water changes, 2 x daily water checks, water filter, always making sure water conditioner was added, and rotate filling the tanks never letting the water temp change more than 3 degrees in 12 hours. The fish will be moving to a 2,000 gallon pond in a few months. I will not put any fish in the pond until late spring and the pond has been cycled completely. I have learned my lesson. Please do not beat up on me. 

Ammonia - never above .25pmm - water changes if ammonia registers

Nitrites - 0ppm

Nitrates - 0ppm

ph range 6.5-7.0

Temp - 70 degrees single 500watt heater

600gph Pump filter - Mechanical, biological, and uv filter.

Matrix biomedia

Seachem Prime water conditioner

Recently started adding API stress coat - 2 weeks ago

I vacuum out all waste daily - Small quite battery powered 

Maximum water change 50% is water has ammonia spike - Rare

Typical water change 30%

Water changes twice a week. More if needed. 

Hikari growth - small floating pellets

Filters rinsed in tank water weekly

All other fish and tanks have the same readings.

Baseline for Tap water registers no ammonia, nitrates, or nitrites. ph is 6, and it is hard water. 


Can anyone help save my fish?????????????






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That’s quite a pickle but we can help you. It’s just time, primarily, that will help the cycle issue. And in the meantime we need to keep the tank healthy and stable.

First step - your water is fairly acidic. We may want to buffer it with some baking soda or aragonite sand which will help the fish maintain healthy immune systems and raise the pH a bit. I like to figure out how many tablespoons per gallon it takes to buffer the tank to about a 7.4, and then I add that amount of baking soda to each gallon replaced in a water change.

Second, don’t bother rinsing the filters in your tanks. You NEED that waste breaking down to cycle it. Just knock the solids into the bucket and call it good, no vigorous squeezing or shaking. And it probably only needs to be done every few days.

The water changes are far more important, when you begin to show more than .25 ppms of ammonia, an 80-100% water change is where it’s at, and it sounds like you’ve done this already? Fewer big ones are better than several small ones, as the ammonia concentration in the remaining water continues to elevate. It needs to be completely removed. I was a little confused by your explanation - is your TAP water high in ammonia? Is that why you’re doing the smaller changes? Or is it spiking over the course of a day - that would be more expected and normal, my own hospital tanks tend to get 100% changes once daily, minimum, just because of the ammonia rising after their feeds.

Finally on treatment, can you hold the fish under bright light or in a glass tank and get me a good profile view? It’s hard to tell much when they’re top down. I do think that right now we need to focus on salt and meth blue to help them gently heal. They may have an infection, but it really looks like lesions from the ammonia instead at the moment. If we do an antibiotic it will be nitrofurazone, which you can obtain here in good quantities to treat your tanks:


But my current recommendation is buffering the water and raising the pH a bit, a .1% salt solution, and meth blue in the water. A week or so of that with the good water chemistry should help them heal a bit on their own, or make it clear they need an additional boost from antibiotics. Do you need more detailed instructions on how the treat the tanks? Please let me know if anything needs clarification.


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