You're problem, if not the whole issue, at least a large junk of it, has to do with that salt. They are notorious for having whacky levels. I would ditch that ASAP and use either Tropic Marin Pro or ESV salt.
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any salt mix you use is optional. I used rc for 6 yrs in a row, then instantly switched to io with my 100% water changes, mixed lps and sps reef, then switched to every other brand my lfs uses which ranges greatly in calcium and alk variables.
what salt to use is in the top 4 most debated items in reef web history along with should I pinch a puffer, should I skim or use plants, and is UV bad or good.
nuances are all that become of the choice of salts, but for a non testing water change heavy feeding corals so thick you have to break them off to make room, nuances will not matter.
since we have tanks of the month using instant ocean only with all its low levels, and these tanks house lps and colorful sos, that shows salt choice isn't a make or break at all compared to feeding of diverse offerings.
100% for sure
if you take any practical salt mix sold you can change out 100% of my water to that mix, regardless of brand or measure, and my corals will not mind. ive switched brands 15 times over the years not even knowing when the lfs changed out the last batch for something cheaper for them to bulk sell, its been every name brand known except for the real high end ones lol/
I've seen first hand what tanks using ESV and Tropic Marin look like. Full SPS tanks with minimal dosing. Take me for an example, I had to do dose my tank to kill digitate hydroids. I was trying the Red Sea Coral Pro Salt..the black bucket. The problem with that one is, the ALK is almost 12. Once the dosing was complete, I had to do 3 large water changes. 50-60 gallons for three straight days. Instead of using the black bucket, I used the blue bucket (still Red Sea, but I forget the exact name). My coral looked terrible. As soon as I figured out it was the salt, I did small water changes with TM and they came right back.
I saw you are measuring calcium with a "meter". Several have reported large inaccuracies in measurement of calcium with that instrument.
Perhaps it might be worthwile to have the calcium but also alkalinity measured using a titration kit. Perhaps at a LFS or by a friend.
Perhaps the corals closing could be due to a low alkalinity or low calcium.
If the concentrations are highly skewed and adding both might not necessarily correct the situation.
Yes, but I would do such over a longer period than 3 days. A week would tell you more.For example, if I measure 3 days of alk and cal dropping a certain amount do I then just take an average of total depletion divided by the 3 days it has been?
At least a week after getting Mg back up, but two would be better.How long should I let the tank go and how often should I test before starting dosing again?
When you see consistent daily consumption over a week's time or so.Is there a "sign" that points to when it would be okay to dose again?
I saw you are measuring calcium with a "meter". Several have reported large inaccuracies in measurement of calcium with that instrument.
Perhaps it might be worthwile to have the calcium but also alkalinity measured using a titration kit. Perhaps at a LFS or by a friend.
Perhaps the corals closing could be due to a low alkalinity or low calcium.
If the concentrations are highly skewed and adding both might not necessarily correct the situation.
I noticed that as well. IMO the Hanna Cal checker makes a great paperweight but a poor calcium test. I would put far more trust in licking the water and making up with a calcium level off the top of my head.

Yes, but I would do such over a longer period than 3 days. A week would tell you more.
At least a week after getting Mg back up, but two would be better.
When you see consistent daily consumption over a week's time or so.
But I also agree with some others too; there's really no need for you to be dosing at all for now.

I mentioned earlier about salinity. Did you recalibrate your refractometer? With calibration fluid or rodi
I only have with RO/DI as I don't have calibration fluid on hand. Any idea if I can cut down the levels of Randy's DIY calibration fluid and net the same results? Dont have a 2 liter bottle hanging around the house.
Not sure. I'm not familiar with the DIY solution. I remember reading it before but that's about it.
I have read and seen more then a few tanks having very similar issues to you. People chasing numbers, way overdosing, and pretty much sending the tank even further downhill only to finally give in and get the proper calibration solution and find there salinity way off.
Without salinity being right everything could be wrong.
I'd be willing to bet a LFS near you has it available if not possibly someone in a local reef club. It's a pretty common thing for reefers to have on hand.
Did you test the newly mixed saltwater yet, just curious what kind of reading you are going to get on that

