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My fish have been in my tank for about 3 months. the tank is 300 gal. all readings are at or about zero. Water temp is about 78. Over the past 4 days they have been dying off. I have checked everything and can not find any reason for them to die. I added about 15 new fish about 2 weeks ago. They were from the same breeder. I also tried a new food. I'm thinking the food but am not sure. Any help or suggestions would be appreciated.

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One of the veterans will step in here. 

My guess is you over loaded the bio-filter with the addition of 15 new fish.  You might have done it too quickly and just over loaded.  This is if you can rule out disease. You might want to prepare for a partial water change maybe like.  Test water again.

Readings at Zero seems a bit strange to me.  I always test about .25 ammonia and a little nitrate.  PH certainly shouldn't be at Zero.  

Stop feeding is usually a first step.

I'm sorry, I wasn't thinking about the PH readings. They are at 7.4. My ammonia readings have been either zero or .25ppm. My nitrates dropped to zero after I added my fish. I was told that was normal due to the fish being small and the plant growth in the growbeds was quite active. I can see nothing wrong with the fish except for the dead part. No signs of disease. I have stopped feeding them as of yesterday.
George said:

Readings at Zero seems a bit strange to me.  I always test about .25 ammonia and a little nitrate.  PH certainly shouldn't be at Zero.  

Stop feeding is usually a first step.

Was there enough oxygen content for the fish? (Are the fish mouth open when the fish died?)

How do the fish look like when they die? (Any white spots or obvious sings of disease, how about ripped fins?)

How where the fish condition before you moved them? How did you move them?

How many die in one day?

Are you using city or well water?

Is there anyway any kind of chemicals could of gotten in the water?  

Sure hope Miriam comes back with an answer to WaterFish22's questions, the fish food mentioned, and an overall report as to what eventually transpired.

I am having the same trouble.  I'll post my results in here just as added info and will report back on the end results for me.


I added 18 blue tilapia fingerlings to my 160 gallon system in Feb.   They were happy and growing like crazy.  Some were over 3"  in a month so I moved to the stage 2 aquanourish feed mixed in w/ a little crumble for the smaller fish. 

2 days ago, they started dying fast.   3 the 1st day, 2 yesterday.  2 look like they aren't gonna make it thru today.     

The smaller ones are dying.  The larger ones look sick.       They seem to be gasping a bit but not at the surface.   They look gray-ish.   They are lethargic and can't swim well and just look horrible.   They have trails of clear trails of waste coming out the poop shoot.  

The system is well over a year old and my goldfish are still healthy.   My water is city water that I filter thru Brita to bring down the PH, soften, and remove chemicals.     I did have a full ammonia test vial fall into the tank.  But at 160 gallons, I can't imagine that was it.     

Readings were good.

 ph 7.2 ( brought down from 8.0 over 3 weeks ) 

 ammonia ( 0 to .25 ) 

 nitrite 0 

 nitrate 80 or so.  pretty rich but not overly so. 

My best guess to what I did wrong is overfeed with the new stage 2 Aquanourish.  I noticed a week after I started feeding them this food that uneaten food was collecting on the bottom behind rocks and in corners.   It was rotting and had a fuzzy  , mold like appearance.  A pretty good amount.   I used a powerhead to push that out into the system and it either got eaten by my goldfish or made it to the growbeds.  

Action plan: 

 changing water in 30 gallon increments over the next few days .

 stop feeding for a couple of days then slow way down in how much i give them. 

 when thing stabilize, replace dead soldiers and move on. 

They look gray-ish.   They are lethargic and can't swim well and just look horrible. ==> I wonder if you have a fungus on your fish. Do they have a gray-ish like cotton fuzz on them? 

Nitrate 80 or so ---> Try to keep the nitrate at 0 or below 5.0 if at all possible. I have a test kit simple test kit and it ranges from 0 to 180PPM. Most fish I was told like it well below 20PPM it depends on the species at least that's what I was told.

I have 25 tilapia and I have a non connected system. Meaning that I pump the waste water off of my tank to my garden or growing beds and the water doesn't recirculate back to the fish tank. I like my system becasue, then I can keep the water almost crystal clear in my tanks. I have only lost one tilapia fish after it jumped out of the tank. My fish are now 3 to 4 inches in size, no babies yet!

Yeah, don't over feed them, I feed my fish 3 times a day and I only give them as much as they can eat.

No fuzz.    Just dull in color and definitely stressed.    Thanks for the reply.  I have 3 full, super healthy, 3'x2'x10" grow beds ( lettuce, tomatoes, basil, peppers, parsley, beans)  and even then I seem to have to do water changes to keep the nitrates down.  I read that 80-100 is not toxic but I'll step up the water changes and maybe try to add in a 4th grow bed.    From my reading this morning it def seems to be an overfeeding issue.    Poor lil guys.    Hopefully some will make it and reproduce. 

Here's what my system looked like on 3/6.   Plants are much bigger now and fish, well, you know.

 Yeah, I don't know the size of your tank but, I found out that the larger the tank you have the less prone it is to disease and other problems with your fish. If you do more water changes you just are watering your garden or gowning beds so using more water can't hurt. I got my fish in October of last year so, and I have them in two different tanks over 100 gallons, if everything goes right I hoping they will start beading in 1 1/2 years.


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