Hanna Phosphate checker

[Dave3112]

Well, Saturdays are my maintenance days on my tank as I'm sure it is for some of you too. This includes checking the parameters I test for (Alk, Phos., Ca and Mg). Also for water changes and, if needed, soaking a pump or power head in vinegar and cleaning it. Anyway I checked my Po4 with the Hanna checker and it read .14!!! I almost fell out of my chair! I run GFO in a reactor and change it out every 2 weeks so it shouldn't get that high unless I have lost something. So I decided to check it again and it read .02 that time. Well that is more inline with what it should be but was WAY off from the first reading and well, I wanted to check it again.....so I did and it was .05?! Which one should I believe? All of these were preformed in less that 3 minutes so the reacted sample didn't sit too long. So what is the deal? BTW I use 2 separate bottles to run the test. I put un-reacted tank water in one and the reagent and tank water in the other.

 

[Tomoko Schum]

To be accurate with a spectrophotometer like Hanna checkers, you should complete the whole test using a single cuvette. Every quartz bottle/cuvette is slightly different in composition, thickness, and what have you, and it can give you some variation in results if you use two different cuvettes. However, the type of variation you are having indicates an error in the test squence or the amount of an reagent added.

I actually had a very similar situation before with three varying results, too. In my case, I was making an error (being inconsistent) in the button pressing sequence. Some people reported that it is hard to get all the reagent powder into the cuvette. I also make sure that the bottles are cleaned very well each time since the checker is measuring such a small gradient/concentration.

 

[Dave3112]

That could be so with the cuvette. But wouldn't the reading be consistent? If the same 2 cuvettes were used? I may get another PO4 test kit to check the meter with. I had one a while back but it was expired and I threw it out a few weeks ago. what is a good one to get? I like the Elos Ca and Mg are the PO4 ones from them accurate?

 

[Tomoko Schum]

If you are using the same cuvettes consistently, you should get the same results, having the same offset. I'd look for inconsistency elsewhere, then.

 

[H@rry]

I had the same thing happen last week. The first test came out @ .11. I didn't believe that and tested again and got .02. I tried very hard to get all the reagent powder into the cuvette but I probably left some in the corner and I notice a little spill. I also think it might have been caused by not wiping the outside of the cuvette very well before putting it in. I think a salty fingerprint will throw it off.

 

[Dave3112]

I found the trick to getting all the reagent in the cuvette I'll show ya Monday when I bring the reactors to you. I picked them up today. I keep a golf towel in the fish room and wipe all the cuvettes down before I put them in the checker because I noticed the bad readings when I first started using them. So I wipe them down good now before the test and after I rinse them out when I'm done. I don't know why I am getting such different readings. I am buying another PO4 test kit here in a few minutes to double check the meter after it comes in.