I'm not entirely certain I follow, but let me see if I get this right. Traditionally, you have relied on your makeup water to maintain alkalinity; lately, your makeup water has less alkalinity than it used to; consequently your tank alkalinities are lower than where you would like them to be.
Well that seems rather odd to me. Given what you say, if your RO/DI was spot on before, and it's spot on now, then the difference must be the salt itself. New recipe or just a maybe a luck of the draw bad batch?
But I wonder if it makes sense to dwell on the reason, because to me alklinity is one of those things that gets used up rather quickly, and the consumption accelerates as things get more numerous (or more realistically, they grow and get bigger). It seems to me, and this is only my opinion of course, but if you're taking good care of your tanks, alkalinity by makeup water is going to eventually face a point of diminishing returns. You might need to start looking for other means of replenishing alk. Two part additives work well but if you're already married to your tanks that won't help (ie., one more thing to fuss about on a daily basis); then there's kalk, cheap like borsht (sp. ???) but not entirely risk-free, or there's the homemade buffer solution (yeah but it's washing soda .... ???
) .. or there's the calcium reactor idea.
I dunno ... it's just an idea I throw out there.
"Calcium reactors ... they're not just for SPS tanks anymore!!"
