Possible Trace metal contamination for mixer?

aarbutina · Sep 3, 2017

So I have been puzzling over why my corals haven't been doing so hot recently and I am wondering if this could be a possible cause....

I normally mix up 5 gallon batches of new salt water when I do a water change. A couple years ago I grabbed a mixing motor when we were cleaning out our lab at work. When I set my tank up I purchased paint stirrer to use as the impeller. The actual head of the impeller is plastic but the body is metal. At first I didn't think much about the metal because it would experience limit contact time and I thought it was stainless. Not I am finding it is becoming pitted even with and after use rinse, and I am beginning to think it may just be chrome plated. If metals are leaching for the shaft it would mean that ever time I mix up new salt water I am adding more metals... thoughts?

I am already thinking that I should just switch to using a spare power head to be on the safe side but would still like to hear if anyone things that this could be causing some issues.

rayjay · Sep 3, 2017

If that is happening, you could do a good cleanup job on the shaft and then coat it in an epoxy or fiberglass to prevent future contact with the metal.

Paul B · Sep 3, 2017

I personally would not worry about that in the least. That shaft is probably chrome or nickel plated steel which will not hurt anything even if you left it in your tank, but the short contact time you are using it will do nothing.
(Galvanized shaft is a different story and I would not use that, but I can't see well it from here. ) I realize most people will tell you to keep all metals out of your tank, but iron is actually good for your tank, not that any of that shaft is dissolving into your water. If it is a galvanized shaft, the zinc is almost as bad as copper and I would not use it.
If it is a concern, you could put shrink tubing on the entire shaft, I use that all the time.
If you are having coral problems, I would look at something else.

aarbutina · Sep 3, 2017

I know I am grasping a bit at straws here but I have been puzzling on this for a while. Just searching for ideas of leads to chase down. You are probably right that it isn't galvanized steel. It doesn't have that look. But since I don't know what it is exactly I can't say for sure.

Randy Holmes-Farley · Sep 3, 2017

I can't be sure what it is made of or whether that is likely to be an issue.

What is the observation with the corals?

aarbutina · Sep 3, 2017

Randy Holmes-Farley said:
I can't be sure what it is made of or whether that is likely to be an issue.

What is the observation with the corals?

Hey Randy, with the SPS the there is a complete retraction of polyps and as well as STN tip down. Zoas have decided they want to stop opening and are shrinking. Also lost a couple clams the just started gapping for no real reason and when belly up (clams being a bit finicky and as you know can do that with almost no know cause so take them with a grain of salt).

No major alk swings. Been operating between 7 and 8.

Hans-Werner · Sep 4, 2017

To me the oxidation looks like zinc and zinc oxide (the white spots). We had a galvanized rack that looked similar after contact with saltwater. This might very well cause problems. I would either coat the shaft with epoxy resin (or shrink tubing and epoxy resin for the gaps) or use a power head. For small quantities of epoxy resin you can buy epoxy based two component glue.

aarbutina · Sep 4, 2017

Hans-Werner said:
To me the oxidation looks like zinc and zinc oxide (the white spots). We had a galvanized rack that looked similar after contact with saltwater. This might very well cause problems. I would either coat the shaft with epoxy resin (or shrink tubing and epoxy resin for the gaps) or use a power head. For small quantities of epoxy resin you can buy epoxy based two component glue.

Thanks for the reply. I used a couple our maxijets to mix my salt batch yesterday. It took a little bit longer than usual but that's ok. Even if it isn't zinc it makes sense to coat it. Better safe than sorry. I like using the mixer because it is just so fast and easy. But I wont be using it again if there is metal/water contact.