max pH for calcium reactor effluent

[salty joe]

I plan on dripping my calcium reactor's effluent into 2' of 2" PVC with an air stone delivering fresh air. With such slow flow through the PVC, I'm concerned I might raise the pH enough to cause precipitation.
What do you think is the max pH I should allow to avoid precipitation?

 

[Randy Holmes-Farley]

The answer is not at all precise, but I'd guess that if you raise the alk to 25-30 dKH (which is about 3.5-4.3 times the level in natural seawater water) that if you keep the pH below 7.6, the chance of precipitation will not be appreciably higher than in a typical reef aquarium at pH 8.2.

I'd suggest just trying it, and if it's a problem, back off on the air flow rate. Once precipitation lays down some calcium carbonate, it will accelerate on top of the old calcium carbonate, so it might need to be cleaned out if you get precipitation and then want to restart with less air.

 

[salty joe]

OK, thanks. So, if there's precipitation I should see it on the PVC pipe?

 

[Randy Holmes-Farley]

OK, thanks. So, if there's precipitation I should see it on the PVC pipe?

I think that’s more likely than precipitation of new suspended particulates each time because the existing precipitate on the sides acts as a seed crystal for more precipitation.

 

[salty joe]

Would car wax (or something to make it slick assuming it's reef safe) on the inside of the PVC pipe discourage crystal growth? Then, I could hang a fiberglass rod inside the pipe to easily check for crystals and not worry about cleaning the pipe. Would roughed up fiberglass be more likely to attract crystals than smooth?

 

[Randy Holmes-Farley]

I don’t know what is most likely to attract and hold calcium carbonate, but I’ll note that many of these things are not intuitive. Rough might be worse than smooth, but pvc is already hydrophobic and I wouldn’t assume wax is desirable.