Huge difference in test results bw sump and display

[Cment]

I recently upgraded my tank about 2 months ago which I used all my old rock, roughly 20lbs and about 30lbs of dry base rock. I have been testing Mg, Alk, Ca almost daily with salifert test kits to find out consumption so I can set up my dosers. While testing, I was getting a huge difference in daily numbers. I was obviously confused, thought it was my test kits so I went got new one, same thing. Well this morning, I originally tested from the return area of my sump which is pretty low flow bc I have a refugium, getting low readings on all 3. Mg=1125/alk 5.2/Ca 275. Knowing this cant be I decided to test from the display and then got these numbers Mg=1515/alk 8.1/Ca 415. I then tested 3 more times from the display and got roughly the same numbers. Can someone explain to me why such a large difference in readings? Is it all do to flow?

 

[Randy Holmes-Farley]

It must be testing error, unless you are testing directly downstream of a fresh water top off input. None of the big three will vary around a tank system to the extent yours appeared to. There is just no possible way for calcium and magnesium, for example, to decline that much.

I'd take a sample from each location, and test them side by side at the same time to be sure the methods are identical.

 

[Cment]

Well, LOL my ATO feeds right to my return! dang I cant believe I didnt think about this. I bet thats where the issue stems from.

 

[BaritoneJP]

Great example of a great community like R2R ... a collective brain and wonderful, helpful people.