[Wheelman76]

Originally Posted by Delphinus

I want to drill a little into this. I can't remember if you mentioned this already, so if you did sorry for asking again, but ... apart from the readings, what are you doing for PO4 control? Are you using GFO, if so, how much, and how often are you changing it out?

The reason I ask is that I use the same Hanna tester for PO4. The tested results always show nominal values for PO4 in the end (the Hanna ULR tester reports in ppb of P, to convert to PO4 you have to divide the reading by 1000 and then multiply by 3.0666) but even so, I notice problems with SPS when I let my GFO get too old.

As far as PO4 goes, I am absolutely convinced of 2 things:
1) Most SPS problems we see and especially those that we can't easily rationalize away to something else .... are usually PO4 related.
2) Testing for PO4 is just something we do to make ourselves busy but the results are meaningless. You might as well dip your finger in the tank, taste it, then emphatically state the first random number that comes to your mind. (It's important that you state it emphatically, otherwise you have to do the test again.)

It might not be THAT bad but OTOH, I think it's closer to the truth than we'd care to admit. I think it's getting into the territory of inorganic phosphate versus organic phosphate and how our test kits and testers can only give you readings of one of those (I forget which), but the SPS are inhibited by the one we can't test (we just hope that if we test for one, that the other is going to be reasonably close).

I notice a definite correlation in how well my corals are doing if I change out my GFO every week, versus at slower change out intervals. Unfortunately the cost of GFO and especially at my tank size (280g) it is quite cost prohibitive to be changing it out every week, so this is something I tend to get an "opportunity" to observe repeatedly. If I get all gung-ho and change it out every week, my SPS grows well. If I don't then .. not only do they not grow well, many will recede or let go altogether. It can be as little as letting it go one or two extra weeks between changing out my GFO.

And yet, the Hanna tester will repeatedly tell me that PO4 is not a concern because it will be 0.02 or something so low that it's in the "it can't be PO4 that is the problem" category. But like I said, I'm convinced that it probably is to blame for a large majority of otherwise-unexplainable SPS problems seen in the hobby.

Not arguing with you about po4 levels , and I change my gfo every month and my Hanna checker always reads less than 0.02. But here is an interesting article for everyone to read on the subject of po4.

http://www.reefsmagazine.com/forum/r...phosphate.html