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Our water company tells me that there is 44.7 mg/l  of chloride in our water. Is that high enough to kill tilapia? Many of my fish are dying and I'm trying to figure out why. 

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Chloramines = dead fish.  Did you do anything to get rid of the chloramines?

Oh sure. I always added Chlor-AmX to the water. I have done this for several years with no problem at all. No problem. Suddenly this year, big problems. 

First off, I am sorry to hear about your fish losses.  I am sure it has been very upsetting and frustrating. 

2nd, here are some questions to help move towards finding a cause:

  1. Type of fish? Number of fish lost?
  2. # of gallons in system
  3. How fast did it happen?
  4. Sign of issues with fish (torn fins, lesions, poor body shape, fuzzy stuff growing on body/fins)?
  5. Have you added any new fish recently?
  6. Used pesticides/herbicides in any manner?

If you have the money, I would highly recommend getting your source and system water tested.  The place I use costs about $40 per water sample.  This would help rule out any water quality issues (too much copper etc.).  It does not rule out viral, bacteria or fungal issues.

Hope this helps!

1. Tilapia. Lost all 25. 

2. 300 gallons

3. Over a period of 4 weeks. Generally one or two fish a day. 

4. None of the things you mention. A couple of them had red areas around the gills. I have attached a photo. 

5. No. 

6. Used mycotrol, Bt, in the garden beds but they are isolated from the fish tank. I am careful to not get the pesticides in the sump water. 

P.S. Plenty of aeration. 


What sort of temperature control do you have in place?  What was the fish behavior before dying? Gasping at top, flashing, etc.?  The fins/gills look a bit red but that might just be aspects of tilapia - I am not as familiar with them.

What's the pH of your source water?  I was looking at the Florida Aquaduct report and it was showing in the 9s... but your pH is 6.5?  Do you treat the pH before adding top up water?

I am at a loss as well for what the cause is... I would recommend at this point getting the water tested if you can.

I live in the Florida Keys and the temperatures here are consistently in the 80s so that's no problem. I do adjust the pH with Aquaponics Source's pH down product. Yeah, it's very high pH. 

I'm at a loss too. I've been doing this for four years with no problems and then BANG! I am getting the water tested. Thanks so much for your help and concern. 

You may want to check your phosphate levels when you get the water tests back.  Due to your really high pH, you may want to alternate between using phosphoric acid and hydrochloric acid(muratic) to avoid adding too much phosphate to your water.  I don't think this is causing your fish deaths but it can certainly cause other issues with your plants - nutrient lockout is common when using phosphate buffers in addition to increased likelihood of photo-toxicity.  Another option would be to use RO water.

I'm thinking seriously about RO water. 

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