Mystery magnesium
 

SO this tank has been set up since April. So far, I've not dosed a single drop of magnesium, and yet I've never had a test result come back below 1400ppm, averages around 1440. I thought it was my test kit, so I bought a new one and same result.

I'm dosing arm and hammer baking soda for alk, and was previously dosing a bulk anhydrous calcium chloride solution but recently switched to Kent turbo calcium (effectively the same thing) because I ran out. Is there magnesium in either of those two things? i'm also using H2Ocean salt, which I find to be pretty high in magnesium to start with, but before and after water changes my levels bump from the 1440 range to the 1480, 1500 range, and then barely fall between water changes.

Any ideas?

Same thing happened to me with the 400 and now the 28. Never had to dose mg and it was always 1400. No idea why.

What were your calcium and alk dosing chemicals?

yup, just tested again, 1410

Mystery magnesium
 

I would expect there will be no Mg in either baking soda or CaCl (anhydrous or otherwise) unless it says on the bottle (bulk would be really unlikely). I would suggest you are either making the same mistake with two test kits and getting an erroneous reading (not likely), or your WC water has high Mg levels. It's easy to figure this out... just test the new ASW before you do your water change. If you are really wanting to verify things, test your tank water just before and maybe an hour after your WC along with your new ASW. You should be able to predict what your tank should be at after the WC.


Dan

I used BRS chemicals and reef crystals. H2ocean now. I actually never test new water. I dialed my dosing to take in the effect of weekly changes. All 3 levels were very stable.

I have heard that people using H2O salt and who do regular water changes don't need to dose Mg. That is why I switched. So far what I have heard has held up.

I took a look at your build, I wouldn't expect your tank to go through a lot of Mg, back in the days of the massive Mg crashes we used to have about 2lb per gal of rock, and cramed full of SPS, and DSB even at that point my own tank never developed Mg problems for about a year. I had a 8" DSB, 240lbs of rock in a 90 gal tank, and every inch was filled with SPS.

I noticed a while ago the trend now is more open tanks and thinner sand beds, and I also noticed people stopped posting of low Mg. Keep an eye on it but I don't suspect it will take more than the odd addition during water changes.

but then I could be wrong also :mrgreen: just my 2 cents

Steve

Mag can be weird sometimes. I have had times where my system uses a ton of Mag and then demand drops off and I don't dose any for months on end. Then the Mag will drop off and I will start dosing again.

Yah I'm wondering if it's this salt. I really, really love this salt. I just wish they would drop the price by about half and start carrying it in more places in Calgary!

You think the amount of rock and sand contributes to the rate of magnesium use? Do you think that's because there's more calcareous surface area for it to react with, or because there's more biological activity that uses it going on?


Also, before bed last night I cleaned out my calcium and alk reservoirs (they're attached to my sump and I haven't cleaned them since the tank was set up), and wouldn't you know it, I found a large wood screw rusting to death in the bottom of the calcium vessel. It has to have been there since almost the first month the tank was set up, as I haven't screwed anything in around it since then. is there magnesium in metal screws?