[Delphinus]

(Thanks Greg!)

Well.. second weekend of switching to GFO, so thought I'd test PO4 again.

Tank seems to be 0.09 now. GFO outputting also 0.09, so seems steady so far at replacing weekly. Still only 1 cup of GFO, however, which is like 25% of the recommended amount, so perhaps this makes sense. In fact the more that I think about this, I'm not sure what putting more GFO in the reactor does beyond lasting longer (ie., if I put in two cups would that mean it could last 2 weeks instead of 1, but the PO4 absorption remains the same in either case? If so then it just comes down to a question of how often does one want to refill the reactor.) The only thing I can think of is that if one could safely reduce the PO4 down to undetectable levels, then using more GFO maybe means you can have more flowrate through the reactor as well, thus increasing the reactor's ability to remove PO4 as it is produced ... however if you're already at or near zero then I'm not sure what additional benefit there is to doing that in the first place. In no scenario does one really get to leverage the GFO.

At least one can decisively predict the amount of GFO needed however, which is kind of nice. The only thing left to figure out is how many cups are in a lb. of GFO, after that I should be able to predict down to the week when I'm going to need more GFO.

One thing I am noticing with the Hanna tester however is that about every 2 or 3 tests, I get a total wingnut value. What is weird is that it produces the same wingnut reading every time. At least the silver lining is that if I see this value, I can pretty much just say "yep bad test", dump the vial and start over.

The Hanna tester "ULR Phosphorous" ("ULR" = "ultra low range") gives you a reading that says "ppb" (parts per billion) but what's important to note is that it is "ppb phosphorous". To convert to ppm PO4 (which is what most of us reef aquarists tend to think of for PO4) you multiply by 3.066 and then divide by 1000.

So my earlier reading of 0.08 corresponded to a value on the tester of 29: 29 * 3.066 / 1000 = 0.088somethingsomething which I just round up to 0.09.

When I get one of these wingnut values, the output reads, almost always, 55. There have been a few cases where it wasn't exactly 55 but close. So basically now if I get a reading of 55 to 59, I discount the reading, dump the vial, clean it out and start over.

What really tipped me off to this was that I got a GFO reading of 55 once which was higher than the tank. I would expect the value to be zero, or at least zero, or the same as the tank, but it should be next to impossible for the GFO to output higher than the tank. The whole reason we use GFO over other PO4 absorbers is that it's not supposed to leech PO4 once it is expended. On the second test it gave a zero reading, which made total sense.

I wonder how many others have this issue. Kind of weird.