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I have goldfish in a 90 gallon tank.  Each day I find a couple dead.  I have checked the nitrate and nitrite levels daily.  They have climbed quickly, and I think that is the problem for the fish.  I have 12 sq. t. of grow bed on a continuous pump and drain system.  Can anyone offer advice as to how I can drop these levels to save fish?

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Is your system new? If so patience is the only answer.

It's about 3 weeks since I have added the fish.  The levels were good before I added the fish.  I started with 30 very small goldfish.   I am thinking that may just be too many.

Richard Wyman said:

Is your system new? If so patience is the only answer.

Did you fishless cycle the system before adding the fish?  As in add an ammonia source and watch the ammonia, nitrite and nitrate levels as they went through their spikes and stuff?  Otherwise having good levels before adding the fish means nothing since the bio-filter needs to be cycle up before the system will easily support lots of fish being fed.


So we need all the info,







Details about your source water (chlorine or chloramine can be a real problem when cycling up a new system.)


How many gallons per minute or hour are you pumping.

How much are you feeding those fish/how big are they.

What is your media.

How much plants do you have going.

How about aeration?


In general high Nitrates are not a problem until you get grossly high (like 10 times more than the chart can even read.)

Nitrite however is very toxic to fish, this can be somewhat mitigated by adding 1 ppt of salt and aerating well but long term nitrite exposure can definitely kill fish.

Ammonia definitely kills fish

pH can be important in all of this as can temperature.  Sometimes fish that are shocked by being transferred abruptly from one set of conditions to another with no acclimatization will get weak and stressed and become prone to dieing from opportunistic infections and will be even more prone to dieing from poor water quality situations. 


Then again, feeder goldfish are often not all that hardy (depending on the place you buy them from, some are the sick and diseased fish that wouldn't survive anyway and are sold off to be food for other fish because they are not expected to survive long anyway.)

Other times cheap goldfish can be tough buggers so it is sometimes hard to tell which situation you are in without knowing more information about your water quality.

Everyone, including myself, started with too many goldfish if we chose that method of cycling. That is why there are so many posts about high nitrites. ammonia and dead fish.  I think one fish per 10 gallons is plenty of feeders to start a system.  You can always get more feeders later if needed.

In order to lower ammonia, nitrite or nitrate in water to save fish the standard choices are,


1- time and patience to let the system cycle up naturally but if the levels are too high this can mean loss of fish.

2- Partial water changes, but this requires having appropriate water on hand (de-chlorinated or chloramine neutralized or pH adjusted well or rain water) to do the water changes with and water changes will generally slow the cycling process if the ammonia levels are below 3 ppm.  If ammonia levels are off the chart, ammonia could be stunting the process and a partial water change may be the only way to get it going again.

Thanks to all!  I did cycle fishless for about 2 weeks prior to adding fish.  I have about 20 fish left, which may still be too many.  Ph level is right around 7.3.  There is no heater, so the water is cool but not cold.  I will get an exact reading and share.  


How many gallons per minute or hour are you pumping.  50 gallons/hour

How much are you feeding those fish/how big are they.  Fed four times a day, average range is 3-4"

What is your media.  Pea gravel

How much plants do you have going.  4 lettuce, 4 swiss chard, 4 basil, 3 tomato plants, 1 pepper, 4 cabbage

How about aeration?  I have 2 feet between grow beds and tank for aeration.  Also, tank is outside and open to air.


I am doing a partial water change today.  I'll let you know how that goes.


If you are running a 90 gallons for a fish tank then you should probably be pumping more like 100 gallons per hour or more especially during cycle up.


I expect you may still be experiencing an ammonia spike but since we haven't seen your ammonia levels it is hard to know.


When you have ammonia or nitrite over 1, don't feed the fish, let the bio-filter catch up, feeding the fish at this point is killing them.

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