# Copper Toxicity, EDTA Chelator for



## dwalstad (Apr 14, 2006)

Forgotten Path said:


> I was reading about that yesterday, but the UV destroying the chelators didn't occur to me. I'll let management know and see what they say (haha, this will be interesting). Does anyone know if you could put a chelator like EDTA in the same solution as sodium thiosulfate? We have an automatic dosing chamber to rid us of chlorine as new water comes into the system... It pretty much runs 24/7 so putting the water conditioner in there seems like an easy solution. Hmmm. Work tomorrow will be interesting trying to convince the managers on all of this...
> 
> Thanks for all your help, Ms. Walstad.


_Folks, this thread is strictly for a commercial system with copper-contaminated water and ultra-clean tanks. In an NPT, you've got so much debris and dissolved organic carbon (natural metal chelators), heavy metals are generally not a problem. _

Forgotten Path, I would go slowly here with the managers and get your _ducks in a row_ before you approach them. This is tricky, politically.

First, I'm almost sure that you could mix sodium thiosulfate with EDTA. The trick is that sometimes (depending on which EDTA you use) you have to add base (NaOH) to get it into solution. Our lab keeps a 0.5 molar solution of EDTA in the fridge.

Second, you don't need much EDTA to neutralize the metals. If your water contains 1 ppm copper, that's only 0.0125 millimolar (1 mg/l divided by 64 atomic weight of copper). The molecular weight of EDTA is roughly 300 (depending on which form you use, so that means you need to add 3.75 mg of EDTA (300 mg X 0.0125 mmoles/l) to each liter of water.

This doesn't have to be exact and you will have to do some experimenting to get it right for your water system. Copper concentrations will fluctuate in tapwater and some of the copper will be in the oxidized, non-toxic form. Then there may be a lag time before the UV light degrades EDTA once you start adding it. I would start out by adding 3-4 times of EDTA for whatever copper is in the water. For example, if you've got 1 ppm (1 mg/l) copper in the water, then you would have to add at least 3 mg of EDTA for every liter of water in the system.

EDTA is non-toxic but I wouldn't use more than what you need for your system to solve your metal toxicity problem.


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## Forgotten Path (Apr 3, 2009)

dwalstad said:


> Forgotten Path, I would go slowly here with the managers and get your ducks in a row before you approach them. This is tricky, politically.


 Yeah, it is. I've already mentioned it to one manager who is normally open to suggestions. I'd like to get her, my manager who is over the fish, and our store manager together to discuss it.



dwalstad said:


> ultra-clean tanks


:rofl: Not as clean as they would like. Some of them are pretty nasty sometimes (not to the point of harming fish, of course).

I'm not sure if the management team would be up to getting EDTA and mixing our own solution. However, if they swallow all of this I'm sure they would "store use" a different water conditioner if Top Fin doesn't contain EDTA. I'm going to try and get my little group together Tuesday if I work (trying to get out of work to go camping ), if not then it will have to be Saturday. I'll let you know what happens...

Thanks a lot for all your help, Ms. Walstad!


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