DIY Alkalinity Test - Returning Sample To Tank?

[chipmunkofdoom2]

I would like to start testing carbonate alkalinity using the method detailed by Randy Holmes-Farley in Reef Edition. I have a smaller tank however, and when I adjust my carbonate dosages I test every day, sometimes more than once. If I test carbonate alkalinity a few times a day for a few weeks straight, I'd be throwing out a lot of tank water using the method above.

I later stumbled upon this somewhat related post, which discusses using HCl to reduce the carbonate levels of salt mixes that have naturally high alkalinity. There are various other posts on RC that discuss the same topic, reducing carbonate levels with acid. This would suggest sufficiently pure lab-grade HCl is safe to add to a reef tanks in small, controlled quantities.

Could I simply "dose" the test sample with enough sodium bicarbonate solution to return the sample to its previous alkalinity, then re-add it to the tank? I am confident this would be safe once or twice, but I don't know if this would be safe over the long run. If I test my alkalinity every day, sometimes several times a day, that's a lot of carbonic acid to potentially be adding to the tank. Plus, I don't know what else in our salt mixes may be reacted by the HCl besides bicarbonate. Boron is one I know of that might, but I'm not sure how significant that would be.

Any thoughts or input would be greatly appreciated. Thank you.

 

[bertoni]

You can scale the water sample down quite a bit. A 50 ml sample should be easy to handle, and even 10 probably is doable. You could look up a 0.01 N HCl solution, as well.

I'm not sure what kind of ingredients might be in a standardized acid solution. It might contain chemicals to stabilize the contents. I'd have to look at a specific product to see what might be in it. I wouldn't assume that it's safe to add to a tank, personally.