Well, I'd consider the po4 "checker" a crappy product. I have the colorimeter and testing has shown it's not much better. As stated above, reefers target po4 levels at .03. The margin of error is .04. So if the Alk "checker" comes out and is only off by 8 dkh, would you consider that good or crappy? Here's a quote from a respected individual:
"When I evaluated the original model using a standard (Hanna by the way) and washing the cuvets and caps with high purity acid solution I got a 3 fold difference against the standard when trying to measure below 1 ppm and two fold difference between different measurements of the same concentration. This second part told me that user variation can potentially be even higher than their specified accuracy."
I can tell you from experience that original one works very well and all reports so far say the smaller "checker" works just as well. I'm just a little mad that I paid $75 for the original meter used when I could have got the checker for $40. I test twice just to be certain and I can tell you that it is never off by more than .01. If my phosphates are .01 or .05 it really is fine with me so the .04 margin is acceptable IMO. I would test with the kits and they always said I had zero phosphates. When I used the meter the first time it read .19.
Also to assume since the margin of error on the phosphate check is .04 that the alk checker will be off by 8 is a leap. You can use the tubes and powders and I'll keep using the meters...:bigsmile: