Hanna ultra low phosphate tester readings?

[tundraguy1106]

Hey,

so I have the Hanna ultra low tester for phosphates. I’m currently battling cyano and trying to get my nitrates and phosphates to specific levels however my Hanna checker keeps giving me readings all over the place. its never done this before.

I know that dosing 5ml of my mixture of monopotassium phosphate will raise my phosphate level .01 per 1ml. However after dosing 5ml and testing, my first reading was .32 ppm. My initial test Prior to dosing was .02 ppm (accurate). I then retested again and got a reading of .09 ppm (accurate). My question is why such a high second reading? This is the second time in the past week I got some ridiculous reading?

My test cuvettes do not seem dirty and I always rinse them with RO water. Anyone else have similar issues with their tester?

 

[Spare time]

Do you wear gloves? I highly recommend doing so when using their tests.

 

[tundraguy1106]

I don’t, but I make sure to wipe all finger prints and smudges off the cuvette prior to placing in the tester.

 

[Randy Holmes-Farley Verified Community Expert]

I'm not sure how you know which readings are accurate and which are not.

Can you go through how you made and dosed the phosphate solution?

 

[tundraguy1106]

I'm not sure how you know which readings are accurate and which are not.

Can you go through how you made and dosed the phosphate solution?

I purchased 500 ml dosing bottles. Mixed a specific weight in grams of phosphate based on my tank volume in gallons (added sump and live rock) to RO water. The calculator gave me how much per ml it would raise my phosphate in my tank. It’s also been accurate since I started dosing 3 months ago while battling dinos.

I also tested and retested and made sure the result in question was only a fluke and not repetitive. I also know by how much I dose, how much it should raise my phosphate in my tank.

 

[Randy Holmes-Farley Verified Community Expert]

OK, I was thinking to check exactly what you did, but without numbers, that isn't possible.

In general, calculated amounts of phosphate are rarely sufficient to get that amount stable int he water as much of it will bind to rock and sand.

As to variability of the testing device, that I cannot advise on. Some folks do have issues.

 

[tundraguy1106]

OK, I was thinking to check exactly what you did, but without numbers, that isn't possible.

In general, calculated amounts of phosphate are rarely sufficient to get that amount stable int he water as much of it will bind to rock and sand.

As to variability of the testing device, that I cannot advise on. Some folks do have issues.

I’m gonna look for some good glass cleaner and try soaking the cuvettes. The last test I did yesterday which seemed accurate was in a brand new one. I’m thinking maybe the one I used had some haze inside which threw off my reading. I’m no expert though.