Sump vs. Display Chemistry?

[penguinexdeus]

So in process of calibrating/checking my Trident accuracy I ended up testing water from both my display (few inches under surface) and my sump return chamber. I get about a 0.3 dKH difference with sump being around 8.2-8.3 and display being around 8.5-8.6.

I thought I was crazy but I ran multiple tests each area with Hanna and Salifert being consistent and in agreement. And also the Trident in sump is saying 8.2. if it were testing errors or kit inaccuracy I wouldn't think I'd get such consistent repeatable results in each area.

Could there be an explanation for why the display is higher? Lights on, overall deeper depth in display? Pumps have been running constantly so it's not stagnant or unmixed id think. 0.3 seems somewhat significant. It's a typical average 75gal tank with 30 gal sump underneath in stand. Dose Kalk and carx to sump. Refugium on opposite light schedule. Skimmer in sump.

 

[Dan_P]

So in process of calibrating/checking my Trident accuracy I ended up testing water from both my display (few inches under surface) and my sump return chamber. I get about a 0.3 dKH difference with sump being around 8.2-8.3 and display being around 8.5-8.6.

I thought I was crazy but I ran multiple tests each area with Hanna and Salifert being consistent and in agreement. And also the Trident in sump is saying 8.2. if it were testing errors or kit inaccuracy I wouldn't think I'd get such consistent repeatable results in each area.

Could there be an explanation for why the display is higher? Lights on, overall deeper depth in display? Pumps have been running constantly so it's not stagnant or unmixed id think. 0.3 seems somewhat significant. It's a typical average 75gal tank with 30 gal sump underneath in stand. Dose Kalk and carx to sump. Refugium on opposite light schedule. Skimmer in sump.

Hanna Checker variance is 0.3 DkH, Salifert who knows. The result differences are not statistically significant. At first glance, we do not have evidence that difference exists. Also, with good flow between the sump and rank, there shouldn’t be a difference. So what is the truth?

I would start with triplicate measurements of sump and aquarium taken at different times of the day to get better statistical power in the data.

 

[Randy Holmes-Farley Verified Community Expert]

Generally, the sump and display should be very close for any high concentration chemical such as alkalinity, calcium, etc., unless you are adding doses of something somewhere (including top off water).

 

[penguinexdeus]

Generally, the sump and display should be very close for any high concentration chemical such as alkalinity, calcium, etc., unless you are adding doses of something somewhere (including top off water).

Top off water goes to sump (i dump into first chamber) so that could be it, but my ATO rarely goes off due to the kalk usage. I'll be testing again throughout the day. I feel like i'm going crazy

 

[taricha]

barring local significant precipitation in the sump, I lean toward test uncertainty.