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Help! School Tank Causing Salt Corrosion on Heat Pump/Mini Split AC Unit in Classroom


scissortail

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Hi Everyone,

I am one of the teachers who hosts a tank in their classroom through the awesome Tanks for Teachers program.  During some regular maintenance of the mini split/heat pump in our classroom corrosion was discovered inside the unit from saltwater precipitation, which means it will need to be replaced.  Our facilities folks have looked into getting us a vent hood above the tank, but that would cost around $5,000(!).  Unfortunately, we either have the find some other solution or remove the tank ☹️.  Has anyone here had a similar problem with salt precipitate?  I am looking for other alternatives before we make the tough decision to break everything down.  Any advice would be helpful!   Thank you!

Deborah Maddux, Klahre House Alternative School

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2 hours ago, scissortail said:

Hi!  This is the 40 gallon tank out in Hood River with the black wooden canopy over the top.

Oh okay I know that tank well. Could you send a picture of what is happening? Maybe even setting a fan on top could possibly be a cheap and simple solution. 

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Unfortunately I don't have any photos of the problem because it is happening inside the heat pump unit.  It was discovered by the HVAC technicians when they had the whole thing taken apart.  I have attached a picture of the setup in the room.  The tank is pretty close to the unit so one suggestion was to move the tank to the other side of the room, which we could do, however our facilities team would like something further to ensure that once the unit gets replaced this won't happen again.

PXL_20210824_214705093.jpg

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That seems very odd, since when saltwater evaporates only the water portion becomes vapor, and the salt is left behind in your tank.  "Salt creep" is not from evaporation, but rather from saltwater splashing or bubbles popping and spraying the saltwater onto another surface.  Near the ocean, wind lifts small water droplets containing salt from the waves and evaporation of these droplets leaves salt aerosols in air.  But without any wind, salt cannot become airborne.

 

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I thought only freshwater evaporates so how can it be saltwater ruining the split mini? Hopefully there is a technician on this forum who can weigh in. If a 40 gallon tank could do such damage, I would think most of us with electronics under our tanks and in our homes would also be affected. Hopefully the school can get a second opinion. 

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I concur.   My sump / equipment room is open air in the garage, and I get extra above and beyond rusting.   

For the inside of my house, I've installed an exhaust fan  that draws from inside my hood, and expels into the garage (or outside).  The whole idea is to draw the moist air (from over the tank) OUT of the room.   This is the model I use, it's nice and quiet and has a speed controller to enable slower==quieter.  (under $100 on Amazon, but checkout this company's website, they've got a whole line of exhaust products)

The key, Draw from your tank hood and exhaust Outside-the-room!   Then the AC unit doesn't get the moisture

  • AC Infinity CLOUDLINE S4, Quiet 4” Inline Duct Fan with Speed Controller - Ventilation Exhaust Fan
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Without exhausting the humid air, you will struggle with that. So you have a couple options to at least mitigate the problem. One would be an air dehumidifier. I'm not totally sure how effective this would be because I'm not super savvy on the scientific mechanics of evaporation, corrosion, and how saltwater factors in.

A couple other things that will reduce evaporation would be to reduce the temperature a bit. Cooler water temps evaporate less than warmer water. You might be able to bring that down to 74 or so depending on what's in the tank.

Additionally, you can use a glass top on the aquarium. This is not super ideal because they get dirty and develop hard water stains and then light doesn't get through to the corals as easily. That being said, if you have low light corals, this may not be a problem. If you put a cover, know that it reduces surface gas exchange, but having a skimmer or at least part of the top open, can help offset that. 

Wishing you the best with a solution! It would be really tough to guarantee that this doesn't happen again. So that definitely puts you in a tough spot. But I think if you can reduce evaporation, you'll reduce the corrosion issues. 

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