red sea test kits variation

kaceyo · Aug 6, 2019

First, I just switched from red sea foundation B liquid to RS foundation B powder. I'd read that it (the powder) is 1/3 the strength of the liquid. Also, I just bought a new refill kit for my red sea alk test. I went a couple days w/out dosing the alk as it took longer than it should have for the new powder alk to get to me so I ran out. BAD! My alk dropped from 8.0 to 7.0 (via my old test kit reagent on both tests. SO... I added 33ml of the new powder mix (3x11ml, the amount of liquid alk I have been using daily) + 7ml more to start slowly bringing my alk back up to 8. I tested the water a day after the new powder mix was used and I tested the alk with the new reagent. It tested at 8.4. How could it have jumped from 7 to 8.4 after a single dose of what should have been my usual dose plus about 20% increase in the dose amount? So I retested using the old reagent and it tested out at 7.6. Whew! It had only jumped 0.6 dkh when tested with the old reagent. Still my new test reagent shows 8.4 and the old 7.6. That's a BIG difference way out of the range of accuracy, supposedly.Both are well before the expire date. Has anyone else found such a large discrepancy between test kits? I have no real idea what my dkh is which makes it hard to make an informed decision about where to keep my dkh! Especially if I wanted to keep it low, around 7.0. Is it 7 or is it 6.2?

PatW · Aug 6, 2019

I use Red Sea Pro version. I use the Hanna alk also. I have not seen that much variation with the refills. But I think that there might be some about .2 DKH or so. But my interpretation of the end point is not any better than that. I would have noticed a full 1 DKH swing.

You might want to switch to the Hanna. Sure you have to bite the bullet for the calorimeter. But the refills are only $10 for 25 tests and no end points.

Generally, my Red Sea Pro reads the lowest. Hanna about .2 - .5 higher and Salifert is higher yet.

I have been toying with making some known standards but haven’t gotten around to it.

homer1475 · Aug 6, 2019

Even with the Hanna, when the reagents start to get to the bottom of the bottle, they read low. Open up a fresh bottle and my reading are usually .5 to 1DKH higher then the old reagent.

I've never tracked it, but I wonder if they supply more then 25 tests and you should throw out the remaining when 25 tests are complete(I always throw out the last couple ml and open a fresh bottle)?

GThompson · Aug 6, 2019

I haven’t found any two kits that could give me anywhere close to the same values

kaceyo · Aug 6, 2019

homer1475 said:
Even with the Hanna, when the reagents start to get to the bottom of the bottle, they read low. Open up a fresh bottle and my reading are usually .5 to 1DKH higher then the old reagent.

I've never tracked it, but I wonder if they supply more then 25 tests and you should throw out the remaining when 25 tests are complete(I always throw out the last couple ml and open a fresh bottle)?

That surprises me. I'll have to keep a closer eye on it. I wish I hadn't run out of test reagent and switched from liquid to powder on exactly the same day, lol. It makes it so much harder to get a handle on.