Honestly I can give an answer to any of it other than it has Been tested and proven in my system for years. I use Reef Crystals which I may or may not do a water change every month. Sometimes I do and others I will go months. I generally only do a water change if I see something has changed in the system.
I rarely test the water, again unless I see something changing. I have it written down and the last water test was 10/24, so about 6 weeks ago. As stated I tested mag today and it was the same as 6 weeks ago and I haven't done a water change since then.
I can't explain it but my Mag never has fluctuation and I use 100% Kalk+2.
Salinity was right on an well.
IMO, it is not hard to explain. Reef Crystals has more than enough magnesium, and magnesium is very slow to deplete if limewater is the only source of calcium and alkalinity (that is not true with a DIY two part that folks might chose without the magnesium third part, but that's another story). So no special explanation is needed other than the starting mix and water changes alone can often maintain magnesium. I didn't supplement magnesium for years using bulk calcium oxide from Mississippi Lime Co., and my magnesium always stayed adequately high.
Let's look at this another way. If you want to supply the amount of limewater you used in your size tank, we can look at your numbers specifically, but let's take a typical example and use Brightwell's numbers and assume (incorrectly) that every bit of magnesium in it gets to the tank. So how much is that?
Well, let's assume that in our test tank we add 1% of the tank actual water volume daily in saturated limewater. In a 100 gallon tank, that is 1 gallon per day.
How much magneisum is in that 1 gallon? That's easy to get from Brightwell's data. The solubility limit of calcium hydroxide is 5.7 grams per gallon at 25 deg (that can be looked up online). So that gallon contains 5.7 grams of dissolved calcium hdyroxide, and Brightwell claims the solid product is 0.15% magneisum.
Consequently that gallon contains 0.15% * 5.7 g = 0.0086 grams = 8.6 mg of magnesium.
So daily addition of a gallon of kalk+2 to this aquarium boosted magneisum by 8.6 mg in 100 gallons = 378.5 L.
So it is boosting magnesium by, at most, 8.6/378.5 = 0.023 mg/L per day.
You said:
"I must note also that I have used Bulk Reef Supply Kalk and Two Little Fishes Kalk and with both I had to dose Magnesium daily. "
So you are claiming that this 0.02 ppm per day of magnesium (which again, never makes it to the tank, but we'll assume for argument that it does) made all the difference, and without it you had to dose every day?
Sorry, but that just isn't reasonable.
If 0.02 ppm per day meets your demand, then adding none for 3 months would only cause magnesium to drop by 2 ppm, which you could never detect with any hobby kit.
