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.