high nitrate level

[james rand]

I'm writing this for my friend who does not have high speed internet connections. He has a 125 gallon tank with some barbs, an arowana, a datnioid, geophagus and a couple of others. Already he had to replace all the fish as they died with a very high nitrate level. Filtration is quite adequate with both underground and out of tank filters. The nitrate level keeps going up despite water changes twice a week. Feeding is with goldfish and some shrimp which disappear immediately. What could be the source of the nitrate and what to do?

 

[waterwatereverywhere]

What kinds of nitrate level is he getting? I'd suggest two possibilities, anyway. First, has he tested his tap water? - several people on here have had problems with their source water already being very high. Second, it could be that the tank is overstocked - impossible to tell without details of all the fish etc, but if you have nitrate continually going up and up then overstocking and/or overfeeding is certainly a possibility.

 

[Bol]

In addition to what wwe said, has your friend done a head count lately? Could be some decaying corpses in there.

 

[james rand]

the nitrate level is 40 ppm. Currently there are 12 fish, but the problem existed before that many were there. There are no skeletons. The tap water has no nitrate. The fish are an arowana, 2 gars, baracuda, 2 tinfoil barbs, 2 cats, a Severum, 2 geophagi, 2 green terrors. They appear ok now, but the nitrates keep rising - not overfeeding methinks.

 

[tstenback]

the high nitrate has to be coming from somewhere and if you are doing 2 water changes a week and still it increases like this then there is a source in that tank somewhere. Something is rotting..plants, food ,fish,shrimp something. What are the other levels in the tank ammonia and nitrite and any others that can be provided. Is there any other type of ornaments etc. Definitely an interesting problem. Keep us posted.

 

[Joviella]

are you completely sure that high nitrates are the problem I recently discovered that my tap water has a level of 30-50ppm of nitrate and with tight control my fish are well........

 

[CFC]

The set up sounds awful!!!! Arowanas and gars are big predatory fish that produce a lot of waste so under gravel filters are about as much use as a ash tray on a motor cycle, for a tank containing these fish you should have a minimum of two large external canister filters. UGF's are fine for small fish but become sludge traps and nitrate factories very quickly with bigger fish and those on higher protein diets.
Also you dont mention his water change schedule, when keeping predatory fish you need to do much bigger and more regular water changes than with ordinary fish, 30 to 40% twice a week is what id recomend.
Also you say there are no skeletones of dead fish how big are these fish in the tank? If there are no bodies id suggest that something is eating the fish.