Mg and SG
 

Adding enough Mg to my water change water bumps the SG up two points. Ie., if I make it 1.025 then adjust the Mg I end up with 1.027.

I figure the TDS making up that 1.025 is better off there so I leave it like this instead of using less salt.

What do others do?

Add IO to 1.025 then the Ca and Mg. Final mix ends up at 1.026.

To be honest I haven't adjusted my water. I found the reef crystals levels are great and consistent. I just made sure when figuring out my daily doses to test levels a week apart a day after my weekly water change both times. I thought this way whatever my water change params are (i know they're really good anyways) they are accounted for in my daily dose.

As far as SG...drops from 1.025 to 1.024 by the end of the week usually and I mix my fresh stuff to 1.026 and so far so good it's all been balancing out.

Tony what salt are you using? my reef crystals test just a touch high for ca, and ideal for dkh and mg.

I've never really tested. My salinity seems consistent all the time at 1.026 even when I dump in 1/2 kg of Mg at once. Interesting to not though.

I generally add 1 cup of mg salt (magnesium sulfate + magnesium chloride) to 27gal of RO water and then enough aquarium salt (about 6 cups) to bring it up to 1.025.

Is there any temp change from when you test the salinity before and after you add the mag? I didn't think mag had any affect on salinity. Maybe mix up a batch of ro water and add mag to it and see if the salinity changes (salt in your mag)?

Tony, you add the mg. last? I have no idea what it does to mine. The magnesium and calcium go into the fresh water, mix for awhile, then 2 cups salt. {5g salt bucket mix}. 1.026 every
time.

Doug, what brand of salt do you use? How much Mg and how much Ca do you add to 5 gals?
Thanks

Instant Ocean.

I broke this down from what Ben, {chemmaster}, figured for his large mixing tub.

23g mix,
150ml magnesium
3tsp calcium

Add to fresh water and mix for a few hours, {originally overnight but found a few hours works as well}, then add salt mix.

So far when following this my magnesium has stayed at app. 1400ppm. No need for additional. I change 5g/week on my 30g, and when it WAS sps. I usually drip kalk when I get around to it, but that was the only other calcium source and mine stays at 420ppm. I followed a similar tactic on my 90g with still 5g water changes, when my sps actually did grow. I will do the same for my 30g sps cube I,m currently working on.

I imagine a tank full of sps, clams and coralline, all consuming calcium would need additional calcium supplement but I,m hoping only kalk will do the job.

5g mix, {mine},
37ml magnesium
3/4tsp calcium

Follow same mixing procedure.

I am of the belief that mixing the magnesium and calcium (if used) in the water first is the best idea.

Then add the salt.