Ideas Please - Tank Water & Ammonia

[mistakes r crucial]

People we know that are running 20 fish tanks off tank water have narrowed their Ammonia problem down to the tank itself, readings of 2-4. The tank is concrete.

With that sort of reading I thought it would be easy, there's something or things dead in your tank but after a professional inspection it was given the all clear.

I'm now completely stuffed as I've come up with everything I can think of, I know concrete can do some unpleasant things to water but Ammonia is non one I've heard of. Help please!

[Merrilyn]

Hi mac. Nice to 'see' you on here :P

I suppose you've done the obvious things like checking the source of the water. Nothing curled up and died in the rainwater tank?

[mistakes r crucial]

Hi Mel,

I hope you had a wonderful Christmas and all is well in your neck of the woods.

Yes, all the obvious ones, they even had a professional tank guy check the inside of the tank but that doesn't give me much confidence. From my own experience unless you physically get in there you can never be sure. LoL, that's why you have younger, skinnier fish room partners that don't mind being tied to a rope swimming around in 5000ltrs of water with a net! :lol:

[ILLUSN]

could there be guano in the limestone of the tank itself?
concrete is limestone, most lime stone was once in or near cave sites ( water cuts limestone into caves) bats like to live (and crap) in caves, could this have been incorporated into the cocrete mix?

4ppm sounds high, but i guess anything is possible, the water source itself could have something dead in it (dead brid in a down pipe or water feed system, contaminents upstream?)

[Nev]

I wouldn't rule out the tank itself, is this a new occurance, has it always had ammonia? Or have they only just started testing for it?

[mistakes r crucial]

Thanks for the replies guys. They only bought the property a few months back so I doubt they know any history of the place. They only recently started looking for the cause because they noticed quite high ammonia readings in some well established/cycled fish tanks.

Personally I still think something is dead somewhere, either on the roof, in the guttering or in the tank itself. 2-4 is a pretty high reading for 5000ltrs of water so if it is leeching there must be bucket loads in that concrete mix.

Is there anyway of testing the concrete?