I tried dosing Amino Acid supplement pills from a vitamin store to my tank a few years back. My skimmer pulled REALLY smelly stuff out of my tank for a few hours after each time I did. I stopped after a few days. The suspension, or pill, that the desired dosing substance (i.e. Ca or VitC) comes in might not be very good for the tank. I suspect VitC might be in a sugary substance for some of them and could OD your tank on carbon, causing a bacterial bloom. This is just one possible way you could mess things up
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+1 on the previous posts, although I have heard VitC is great for Zoas and is not something you will get from water changes. At 10G, paying the $15 for a commercially available product at the lfs that will last you years in that size of a tank might be a better choice should you want to go that way
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Dan