Is it the salt, or the test kit?

[Ruu]

I've been playing with low alk/low mg/high CA in my tank for a few weeks now, and have been taking various steps to remedy the situation with some success. I figured a 20% water change wouldn't hurt too much too though, so I have 35 gallons all good to go, but I figured testing the levels in the freshly mixed water would be a good idea.

I got a bit of a strange reading for magnesium though - CA was ~420, Alk was ~9.3, but MG was only around 1080 which seems rather low. Does this sound plausible, or should I be picking up another mg test kit? All the test kits are more or less new (all less than 4 months old) from Salifert.

Dave

[rljlll]

what brand of salt is it?

[Ruu]

Deliberately omitted. I don't want to start a stupid "brand X is low in magnesium" rumor because of a bad test kit, if it is really unlikely that magnesium could be in that range with alk/ca where they are.

Are there salt brands known to be out of whack?

Dave

[Canarygirl]

From what I understand every brand of salt has a mineral or minerals that is either too low or two high. No brand is perfect. The one I use is Seachem Pro Reef Salt and it is known to be low in magnesium. My most recent magnesium test was 1100 which is about what I would expect. I bought some magnesium granuales to put in my calcium reactor (5-10% total media volume).

[Bri Guy]

What salinity did you mix it to??

[bertoni]

That Mg level is consistent with a few brands of salt.

[melev]

Dave, your test kit is probably correct. Alk & Ca work together with pH, but Magnesium stands alone. You'll see many threads about how people are trying to raise their Mag level.

Your goal should be 3x the calcium level, which would be 1260ppm based on the current test value. I personally try to keep it at 1300ppm or above.

[Ruu]

Originally posted by Bri Guy
What salinity did you mix it to??

I always mix to 1.026, as do most people around here I suspect.

Dave

[Ruu]

Originally posted by melev
Dave, your test kit is probably correct. Alk & Ca work together with pH, but Magnesium stands alone. You'll see many threads about how people are trying to raise their Mag level.

Your goal should be 3x the calcium level, which would be 1260ppm based on the current test value. I personally try to keep it at 1300ppm or above.

I was under the impression, from some of the articles I have read, that lowered Mg could depress alk. That was what started me wondering whether my test kit was faulty, and kind of by extension whether I should stop dosing magnesium in the tank - I am in the process of bringing Mg up to 1250 right now and the low mg could be the result of the salt being too low, or the test kit being off. I broke the 1150 mark yesterday, so I still have some way to go according to the testing, but dumping about 2 litres of B-ionic into a tank with normal mg levels probably isn't a good thing.

Dave

[bertoni]

I wouldn't change the Mg level more than 100 ppm per day.

[Ruu]

I have raised it by ~75 in the last 7 days - "dumping 2 litres of B-ionic in the tank" was a literary flourish rather than an actual intention.

Dave