Backyard Aquaponics
A place to discuss aquaponics

Is aluminium ok for use in a AP system? I need to make a heat exchanger for my solar water heater and Stainless steel is hard to come by.

it depends
AP water is oft salty.
Aluminimum boats are all 'Hard anodised' or 'Marine Anodised' this is a process that thickens the oxidised protective layer over the aluminimum.
Putting raw aluminimum into Ocean water, is ok, but will cause pitting on the surface and slowly destroy the substrate.
Anodising only delays the inevitable, but it works for most ppl.
I don't know what effect aluminimum might have on fish, but I hypothesise that it will be such low concentrations that it wont matter.
If you can get it anodised, do, if not, I would say 'Suck it and see' or 'take one for the team' or some other cliched phrase.

I have not as of yet added any salt to my water. However my tests indicate that the water is some what high in alkalinity. Im looking for some stainless but if I cant find any then I will go for the AL.

I've got some 1/4" round bar in my system that I'm using in a level meter. It has some tarnish on it but is holding up well.

BTW, I also have about 10 feet of 3/4" copper tubing in the system to use to heat/cool the water. It is in good condition and has bothered the fish (yet).

Believe it or not, most boats put into the water are not anodized, the grey coating that appears on the surface very soon is the aluminium naturally oxidising ""rusting"",

Chemically anodising is simply speeding up the natural process in a controlled enviroment, also the controlled anodising can provide a thicker and harder coating becuase it is being forced to corrode fast, it can also be sealed and coloured and so forth

To chemically anodise a boat you would need a tub bigger than the boat to provide the electrical process,

Aluminium for humans is actually quite toxic, and is known to cause bone disorders/renal failure/neurolical problems etc etc

I would personally recommend not to use aluminium for anything that your going to eat, probably bad for the fish but even worse for you,

Do NOT use aluminium in AP, it is just as bad as copper long term.

Imagine fish with memory loss lol.

An aluminum heat exchanger is specifically meant for a low corrosion environment and AP usually tends more to the corrosive.
I'm actually just using a coil of poly drinking water tubing as my heat exchanger. Granted, I'm not heating it up to extreme temps as it is only a pool heater on the roof.

I think aluminium exposure has been linked to Alziemers... but I can't remember...

Aluminum has been linked to lots of things (like the aluminum in deoderant being linked to breast cancer?) Anyway, they still sell soft drinks in aluminum cans though.

Anyway, there are risks and you have to decide on your own what risks you are willing to take.

Ya know, living is fatal.

I personally would avoid any metal other than stainless steel in direct fish water contact. Even if the aluminum isn't going to kill you or your fish directly, if the aluminum corrodes away and leaks whatever was in it into the fish water, that might be an even bigger problem and even more worth avoiding.

I just ordered a piece of thin wall SST tube for a heat exchanger. I decided it was safest. Right now I have a coil of garden hose running through my FT but it doesn't work that well.