Problem with Salifert mag test kit?

saltyphish · Oct 24, 2014

Earlier this week I decided to go to a lfs to look for some new frags and decided to have them test my water to cross reference my test kits. I firmly believe in testing my own water. However, after testing my mag the guy told me I was at 1200 which was a little low. (I was interested in a rainbow monti they had). He gave me some good advice and suggested I dose for mag in my system. Since I did not have a test kit for Mag at home I decided to buy a salifert mag test kit they had. I will not add something to my tank unless I can test for it even though my understanding is it is hard to overdose mag. When I got home I tested my Qt tank and the color never changed to blue or gray indicating to me my mag according to this test kit is greater than 1500. I retested 3 times same results decided to test the main tank since that was what he tested with the same results. I know he used a red sea pro test kit 9 (he was out of them at the time or I would have bought one). My question is why the difference? Is salifert more accurate then red sea or the other way around? I do not dose anything I was using reef crystals for salt mix up until a couple of water changes ago where I changed to kent which I believe has a higher mag content. I was also just finishing a cyano battle so Have done 2 major water changes of about 50-60% with the kent. I usually do a 10-15% water change weekly. Also at the same time my calcium was at 460, alk was 9.8dkh. ph is at 8.1. I know one of us could have a bad test kit. My kit is not expired checked that. Is it really possible my mag is that high without dosing and just water changes? Any thoughts on this is appreciated. Thanks.

Randy Holmes-Farley · Oct 24, 2014

You can use a second syringe of titrant to get to the endpoint. Knowing it never changed vs it changed high is useful.

I'd be surprised if it is above 1500 ppm with no dosing, but some salt mixes add a lot. I haven't seen any recent data on Kent salt to know where it comes out, but RC isn't that high.

Wiinberg · Oct 24, 2014

Salifert kits are usually accurate enough for our use, and some salt mixes really do have high Mg, like Randy mentions. Try testing on newly mixed water. Fx. here in Denmark, a lot of people use Blue Treasure SPS salt, and it is well known to have Mg as high as 1550-1650 ppm.

saltyphish · Oct 24, 2014

Ok. Well I tried another test with the understanding I could use another syringe of the titrant solution (thanks, Randy Holmes-Farley) and ended up not needing it. The solution turned blue this time with the syringe reading .1 ml which on the chart reads between 1470 and 1500 ppm. I went to the website for kent to see what their numbers are posted for mag and to my surprise between a sg of 1.024-1.026 the mag should be 1350-1450. I run my tank at 1-.025 sg so my results are entirely possible now the question. Which test was more accurate? I followed the directions on mine exactly. While I can not say the same about the lfs employee. I truly believe they know what they are doing and trust their capabilities. Is one test more accurate than the other? I used salifert they used red sea pro. Which is better? My rainbow monti seems to be very happy.

saltyphish · Oct 24, 2014

I also should add I just started adding coral so there is not much demand in my tank yet

Randy Holmes-Farley · Oct 24, 2014

I'd trust my own testing over an unknown lfs employee.

Yours is also more likely given your salt choices. Magnesium depletes far more slowly than calcium. Maybe 1/10th as fast. So unless you dose a lot of calcium and alkalinity, magnesium isn't going to be a concern of yours in the near future.

saltyphish · Oct 24, 2014

That is what I was thinking Randy since my tests are a closer match to what the website for kent claims their salt contains. I just wanted to make sure since I am now trying my hand at some sps.