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Like it says all of my catfish died started about 2 weeks ago and now they are all dead, but my koi that are in the same tank look and feel fine and frisky. All the numbers are great and nothing has changed .It has started to get a little hotter here (NC)  but the tank sits half way in the ground so water temp is around 78-80 .  Only chemical used were Hi-yield Thuricide and that was awhile back. Here is a pic see anything wrong?

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It can be really hard to tell what is wrong just from a picture of a fish after it has expired.  When they became sick, did you notice anything about them?  Legions or marks on them?  White patches perhaps?

Columnaris Disease is a pretty common killer of catfish and it tends to be pretty much everywhere.  Some added stress, poor water quality spikes or overfeeding of the fish can bring it on and warming water temps still below 80 F tend to be a prime zone for that bacteria to proliferate and cause the worst issues in catfish.  I've had it hit my catfish before and it usually shows as white patches on their backs but it can infect gills too.  When it hits, I usually reduce feed and do all I can to improve water quality.  I'll cull any fish that seem to be more affected that most the others and I will usually salt the system to about 3 ppt of salt.  I  have had fish recover but if they are badly affected it is better to remove them so they are less likely to infect the others or cause worse water quality problems when they do die. 

I have usually seen it show up in spring as water warms and the fish are eating more and more it is sometimes difficult to judge the feed rates and not over feed.  Other times I've had it happen usually had to do with too much handling stress to the fish (like harvesting or netting fish too often.)  My rule now is no more than one harvesting session per week in a catfish tank because times in the past when I netted fish say two days in a row, I usually would have a dead fish or two the next week.  If I give extra time for them to recover between when I go into the tank with the net, I don't seem to have that issue.

Nitrite level is great?  Speaking from my experience, channel catfish are nitrite-sensitive.  I stocked 60 and 58 died.  However, 6 months later the two survivors are growing fast.

is it 3 ppt ? or 3 ppm ? if ti is ppt what does that stand for ? and  (I thought i would mention the salt needs to be sea salt or some other salt that is iodine free ) A dude at the fish store said 1 tbsp per 10 gallons of water helps the fish but is this to much for plants and good bacteria ?

TCLynx said:

It can be really hard to tell what is wrong just from a picture of a fish after it has expired.  When they became sick, did you notice anything about them?  Legions or marks on them?  White patches perhaps?

Columnaris Disease is a pretty common killer of catfish and it tends to be pretty much everywhere.  Some added stress, poor water quality spikes or overfeeding of the fish can bring it on and warming water temps still below 80 F tend to be a prime zone for that bacteria to proliferate and cause the worst issues in catfish.  I've had it hit my catfish before and it usually shows as white patches on their backs but it can infect gills too.  When it hits, I usually reduce feed and do all I can to improve water quality.  I'll cull any fish that seem to be more affected that most the others and I will usually salt the system to about 3 ppt of salt.  I  have had fish recover but if they are badly affected it is better to remove them so they are less likely to infect the others or cause worse water quality problems when they do die. 

I have usually seen it show up in spring as water warms and the fish are eating more and more it is sometimes difficult to judge the feed rates and not over feed.  Other times I've had it happen usually had to do with too much handling stress to the fish (like harvesting or netting fish too often.)  My rule now is no more than one harvesting session per week in a catfish tank because times in the past when I netted fish say two days in a row, I usually would have a dead fish or two the next week.  If I give extra time for them to recover between when I go into the tank with the net, I don't seem to have that issue.

For salt you use 3 ppt

ppt stands for parts per thousand

Right you want to avoid iodized salt or salt with anti-caking agents.  I normally use the cheapest solar water softener salt or solar pool salt.  Solar salt is generally just solar dehydrated sea water.  Anyway, that comes in like 40lb bags for around $5-$8.

And how much salt, go by weight if you can since measuring by the spoon full or cup full will be inaccurate because the size of the salt crystals will affect how much of it you can fit in a measuring cup or spoon.

Here is a link with numbers to help calculate now much salt you need for a volume of water.

Aquaponics, Salt for fish Health

3 ppt of salt is safe for the bio-filter bacteria no problem (I've known of people who run systems for certain types of fish at 6 ppt.)  And many plants won't even notice 3 ppt of salt.  There are a few exceptions, Strawberries are notoriously sensitive to salt and there may be some other plants that will suffer some from salt at that level but most garden plants are fine with it.  There are some garden plants that are fine with even 6 ppt of salt.

Take note here, do some research about your type of fish before you salt your system.  Some fish tolerate much more salt that other fish.  Channel Catfish can't tolerate high levels of salt and 3 ppt is as high as I ever salt them anymore.  Bluegill probably can't tolerate salt too high either though maybe higher than the catfish.  Tilapia can handle really high salt levels (there is a naturalized population living in Tampa Bay which is salt water.)

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