Yes, the phosphorus checker is the most accurate for ultra low range. It was not available from local vendors when I bought my phosphate checker.

However, the phosphate one is more than adequate for my needs esp when compared to the color chart test kits. Despite the 0.04 accuracy spec, I usually get zero readings until my GFO starts getting stale and needs changing. Then I start getting readings above zero, and when it gets to about 0.04, I stir up my GFO in my reactor. Usually after that it drops back down to zero. If it doesn't, I change my GFO, and then it does drop back down to zero. So with those kinds of readings that follow my actions, am more than happy with my phosphate checker accuracy.

Your experience is called consistent. It has nothing to do with accuracy. In order to know if your device is accurate, you have to calibrate it against a known standard. For argument's sake, your actual PO4 could be 0.2 before and 0.1 after (even though your device reports 0.04 and 0).

Yeah, I can't argue that... However, I have compared it to the color chart test kits (that I still have) and it is still more accurate than them, and that hasn't changed. And I guess based on the behavior of my tank and readings, have no reason to believe that accuracy has fallen off. So for my purposes, I consider it more than accurate enough.

The Hanna checker is just one of many tools I use to monitor and maintain my tank. The requirement for accuracy (maybe granularity is a better term) varies by water parameter. For example, I just use API for my dKH, N03 and Ca. Those test kits are accurate enough for me to maintain the desired ranges for those parameters. And I do have/had the higher granularity test kits for them as well to compare.

But with P04, I found a difference in color and growth of SPS when it reached 0.10. My color chart test kits were still reading zero at that level. So for me the Hanna checker was necessary to get the level of accuracy (or granularity) that I needed for my SPS.

Having said all that, it would be interesting (but not necessary IMO) to go out and get a calibration kit. If I start getting readings that don't make sense, for sure I will do that.

The calibration kits are only $10-12 for the HI713 and HI736 kits.

And where can I get them? Have never seen them at an LFS or Cdn online retailer.

Watchiing this thread with interest. I'd like to goet one too....

I got mine from BRS

Well, I do know that AquaDigital is a distributor for Hanna in Canada...:mrgreen:

He probably has the calibration kits (or access to them). Any vendor that carries Hanna should be able to special order them for you. I don't know of any Canadian vendors that stock them.

Not sure if you are using it correctly, I might have to borrow the calibration fluids and check it out in my Hanna.....:redface: :mrgreen: