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Last week, I had to travel and left my AP system in charge of someone, but by mistake left the pump off for about three days.  On my return, there were many dead fishes, and the water was terrible.  I started changing the water, without waiting for the clhorine  to evaporate, in order to lower the amonia. 

I have one FT with tilapia, and two raft tanks where I have small mosquito fishes to control that.  For the next couple of days tilapia fishes have been dying and mosquito fishes too from the raft tankcloser to the FT.  The mosquito fishes in the farest tank are doing well.

I have tested for amonia and it is way off the scale.  I have resorted to taking water out of the raft tanks and replenish it with a hose directly from the tap.  I don´t kknow if there is still some dead fish in the system, the first day I found a big tilapia dead in the raft tank, and the only way to get there is that it jumped from the FT because they are side by side.

Since yesterday, I have found no dead fish.  I feed the remaining tilapia  for the first time, and they look ok.  Still the amonia is too high.  I need to continue changing the water, and I guess the bacteria in the system are depleted because of the clhorine, and the plants are going to be affected, because are just going to be sitting in plain water.

What can I do to get my system back from this disaster?



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Replies to This Discussion

Hi Juan,

Sorry to hear about your troubles! The more mistakes we have the better AP designs we employ. Consider a toilet float for topping up FT levels? This way only small amounts of city water enter daily so that the bacteria won't be affected as much.

So, as you know, don't feed for the next couple weeks. The system will be re-cycled, and whatever fish remain alive, will allow you to go from there. Tilapia  are really hardy fish, but not indestructible!

Get a big container with aeration going to outgass some chlorine from your water before you continue doing so much water changing.  try to remove as much chlorine as possible so that your bacteria will have a chance to re-establish.

You did the right thing in doing major changes until the death rate subsided. Better to use tap water to get the ammonia & nitrites under control than to let the fish die. Yes, you've no doubt lost a lot of bacteria, but if some remains, it will grow back faster than if you were just starting the system. In the worst case scenario you'll have to recycle your system. Most of us have been through similar situations, so don't feel discouraged. Every trial is a great learning experience (in retrospect).

I suggest continuing with 20 - 25% water changes daily until the ammonia is in the lower half of the color range and the fish are acting OK. And now that you have the worst of the situation under control, as TCLynx said, dechlorinate the water as much as you can before adding it. Then monitor your water and keep the levels in the safe range; they don't have to be at zero.

Stop feeding the fish for a while..a few days or up to a week. Keep an eye on their behavior, but they can go a while without food.  If there's any dead fish in the system, they'll eat that, and this will also help lower the ammonia.

Once the ammonia and nitrites are low enough, start monitoring the system as though you're cycling. Do small water changes any time the numbers start to rise. Over time, with patience, you'll get back in balance.

The plants should be OK through this. They may go through a little growth hiccup, but you'll probably have things under control quickly enough to not have a bad effect on them. Good luck! You're in good company. :)

Thank you all for your advice, they have been very helpful.

I have found no more dead fishes, that is a good sign.  I continue changing the water, but leaving the water that I´ll add at least 24 hour in open containers, so part of the chlorine evaporates.

This is a continuous learning experience, and situations like this make us think in how to improve our systems and avoid or minimize them, and to have a group of people that provide advice and support is one of the best parts.




Hi Juan,

I don't mean to sound negative in any way, but, as you recycle, your system will go through high nitrogen spikes, namely nitrite spikes, the same as when you cycled originally. Remember the fish you have now are already "damaged" and are not as tough as they were originally, so they may or may not survive this second trip. Take heart my friend, i do know how you feel because this very same thing has happened to me twice before 

Find a super-fine mesh bag for delicates (laundry)  fill with activated carbon, rinse with tap water to remove dust, and place in the FT with highest ammonia concentration in a high-flow area for 24-36 hours.  If need be , add a submersible powerhead to add flow to the tank, this should help drop the ammonia.


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