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Article Testing test kits: Hanna High-Range Nitrate Colorimeter for Freshwater + Rocco's Freshwater Conversion Calculator

That's how I was using it previously, too. I should have covered that.

The dilution method doesn't actually help with the calibration curve. it does make it more accurate than just the raw freshwater reading to be sure, especially between 10-25ppm, but this method is still far more accurate. Also. now you don't have to mix separately with an extra vial and extra step anymore! Much easier to just use the kit as intended, and then just plug the numbers into the conversion calculator.

I'm too tired to keep testing test kits for now, but if you can make a few known ppm stocks, you should compare this calculator to the 17mL method just to confirm (though I'm confident)!
 
Thank you for this! Appreciate the conversion spreadsheet. I have a nitrate checker on the way.
The other checker that is great, and as a bonus requires no calibration/conversion for freshwater, is the LR phosphate Checker.
I also use the freshwater alkalinity checker but I’m less impressed with it. Super expensive reagents that give inconsistent results as the bottle ages. It really struggles below 1dkh too, and will show 0 alk when water ph is below 5.4ish. I use it for checking degassed and water change water, but use the Salifert kh kit for the tank.
 
This is a bit unrelated but I did run into a company that rents the Hach DR850 Colorimeter for $55. I believe the Hach colorimeters are calibrated for freshwater. If you want to use them for seawater, there is a seawater calibration process that needs to be done.

I realize it's better to have your own but I have found that I only need to double check my math every once in a while. Renting a colorimeter is not too farfetched for this. The company is: Hach DR850 Colorimeter Rental
 
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I reached out to Hanna for confirmation about their High Range and Low Range Phosphate Checkers, both of which I purchased, because the instructions didn't specify freshwater or salt water, and even led me to believe that they're intended for freshwater use at the least.

Turns out that was correct; unlike the nitrate checkers, they work just fine with freshwater testing.

The High Range is from 0-30ppm PO4.
The Low Range is from 0-2.5ppm PO4.
The Ultra Low Range is 0.0-0.9ppm PO4.

I have both the High Range and Low Range. My tanks usually sit between 5-9ppm PO4, so either I can use the High Range checker without dilution, or dilute the original aquarium water sample with 2/3 RO Water to get an accurate reading with the Low Range checkers.

I'll probably do a whole test and writeup to see how accurate they are against known stock concentrations, but for now they'll do just fine!
 
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I reached out to Hanna for confirmation about their High Range and Low Range Phosphate Checkers, both of which I purchased, because the instructions didn't specify freshwater or salt water, and even led me to believe that they're intended for freshwater use at the least.

Turns out that was correct; unlike the nitrate checkers, they work just fine with freshwater testing.

The High Range is from 0-30ppm PO4.
The Low Range is from 0-2.5ppm PO4.
The Ultra Low Range is 0.0-0.9ppm PO4.

I have both the High Range and Low Range. My tanks usually sit between 5-9ppm PO4, so either I can use the High Range checker without dilution, or dilute the original aquarium water sample with 2/3 RO Water to get an accurate reading with the Low Range checkers.

I'll probably do a whole test and writeup to see how accurate they are against known stock concentrations, but for now they'll do just fine!
I have done testing with the LR years ago, against freshwater test kits, and it was always within the range the kits show.
I have confidently used mine for about 7 years now. Cheap reagents too.
The low range tests up to 2.5ppm and I like to keep my PO4 a touch under 1 ppm.
I find my LR PO4 checker is particularly sensitive to cuvette age/cleanliness and bubbles on sidewall compared to the nitrate and alkalinity checker. I don’t know if the reagent stains faster or something else.
I routinely test cuvettes, without reagents, by zeroing them, then turning them a half turn and analysing to ensure it reads 0. Or by swapping unreacted cuvettes of water with the same process. A run through a hot dishwasher with no soap or rinse aid usually brings them back to clear, but I have had to replace a couple that had been in service for a long time.
 

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