Mg and SG

[Doug]

Originally Posted by hillegom

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.

[littlesilvermax]

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.

[Doug]

Originally Posted by littlesilvermax

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.

and I can say I have followed that advice and never a problem.

[Delphinus]

I do add the Mg and Ca first (after bringing the RO/DI to temperature), but I add amounts that I determined some time ago that would raise a bucket of 24g, already at 1.025 for salinity, to bring Mg to 1400 and Ca to 380. (I retest for determining the amounts added for every new box of bucket too.) It's 30ml of Ca crystals (from Ben), and 15 scoops of 15ml of Mg crystals (also from Ben). It raises that 24g another two points so I end up at 1.027 unless I use a cup less salt. I use IO and I find I don't need to adjust for Alk at all these days.

So my question is - since I add the Mg and Ca first, is it better to add enough salt to make it 1.025 or should I add the same amount of salt that I would have added before if I had not dosed any Ca or Mg?

I've tried other salt mixes and the truth is that every brand - every brand - I found eventually needed adjusting for at least one of the big 3 (Ca, Alk, Mg). This is what pushed me back to IO. If I'm going to test for big 3, and adjust them anyhow, then I'm buying the most cost effective salt. The difference in cost for the additives is far far less than the premium you pay for the upgraded salt mixes. Ie., I might spend $10 more in additives over the year but I'll save >$100 on salt over that year. Anyhow a little off topic tangentially, so enough about that .. The real question is, add Ca and Mg, and salt to 1.025 and stop there?

[PoonTang]

SG is what you want so you need to stop when you get to 1.025 including your additives. That is unless you want your tank to be at 1.027. The SG of the ocean is 1.025 with all of its additives included so ideally we are aiming for that.

[Delphinus]

Well ... I sort of agree with that and I sort of disagree, which is why I ask. The ocean may be 1.025 but TDS is not a generic homogenous "thing", any kind of trace element will affect TDS and thus SG and the "composition/make-up" might be totally different. If IO was intended for example to mix at 1.025 but has Mg less than what I want, adding less IO theoretically means less "other stuff" (other than Mg) which might be negligible or it might be detrimental. That's where I'm not sure and was wondering what others are doing.

[StirCrazy]

are you not getting 380 Ca out of your IO? I always did, weird. anyways split the differance.. do your additives, then mix in salt to 1.026 I always went to 26, over 25.
'
Steve