Different results with different KH test kits...

[5TNYReef]

Hi, this is my first post to reefcentral, though I have had many questions answered by searching through the posts and replies here, so thanks!

I have a 150 gallon reef tank (for about 2 years) which was slowly stocked and now contains about 17 fish and about 12 corals, a mix of soft, LPS, and SPS. The livestock are, fortunately, all doing well. At the recommendation of the dealer who originally helped with the setup, I use the B-Ionic system for Alkalinity and Calcium, and find that i need very large amounts of the alkalinity component to keep the KH to around 8 using the Tetra KH test kit. To make a long story short, because of availability of the testing kits, I recently wound up buying the API KH test kit instead of the Tetra and was shocked at the first test to get a value of 11! I managed to get another one of the Tetra kits and have been doing simultaneous testing of my water and consistently find the API kit and the Tetra kits - which use the same units - to vary about 4 points dKH (the Tetra reading lower). pH is running closer to 8.0 by the test strips which I bought, so that suggests that the lower reading is the correct one. But when I add the Alkalinity component of the B-Ionic to the tank, I see significant formation of precipitation which makes me suspect the KH is actually high.

Any thoughts? Is there any commercially available standardized reference solutions I can buy to test?

Thanks in advance!

BTW - Calcium level is about 450 and, after doing some reading about precipitation, I have started testing Magnesium and those levels are OK, too... So that should not be an issue causing the precip...

[ReachTheSky]

Tetra test kits have been proven to be way off in terms of alkalinity. I remember reading an article that showed they were off by about 30% (!!!). It's probably a safe assumption that the test strips are EVEN LESS accurate.

API tests are much better but most people here with reef tanks use Red Sea, Salifert or Hanna Checker. I would highly recommend investing in a more reliable test kit as alkalinity is one of the most important things to keep in check!

[bertoni]

There are no standardized solutions, unfortunately. If you have a pharmacist who's willing to mix a solution, I think I can find a recipe for you.

I have no idea which test kit might be more accurate. Test kits are a common source of problems.

[tmz]

I have never used the tetra. The salifert and api jibe and I have reasonable conficenc in them. The precipitatin would go with the high alk as you observed.

[5TNYReef]

Thanks for the replies!

[bertoni]

You're welcome!