Any relationship between phosphate and alk?

[AcroporAddict]

I removed continuous GFO use from my 465 reef a couple weeks ago, and have just been testing PO4 with a Hanna ULR Checker. PO4 was trending up at .049, but had dropped a bit tonight.

I tested KH tonight as well, and I usually have a very steady KH range of 8.7-8.8 dKH. I use a kalk reactor with my ATO, and a calcium reactor coupled with a Masterflex feed pump. KH was 7.7 tonight, kinda low for my system. I did the test twice with two different Salifert kits and got the same result.

I do have some large acropora colonies that have only been getting larger, so I was wondering if there could be a correlation between stopping GFO use and the lower KH readings, or if the two events are likely not related? The KH could be that the colonies are just using up more of the alkalinity and I need to crank up the Ca reactor more, I suppose.

I don't recall there being a tie in between PO4 and KH.

 

[bertoni]

If growth increased, the consumption might go up. That's the most likely correlation that comes to mind. It's more likely that the events are unrelated, in my opinion, though. GFO often acts to reduce alkalinity a bit by encourage more precipitation, but that would work the other way.

 

[Randy Holmes-Farley]

Phosphate is measured in total alkalinity, but it is such a small contributor that it won't be noticeable. I'm not sure why stopping GFO would make alk decline. Some base-washed GFO might temporarily boost alkalinity, but that effect would only be in the first few minutes of use.

I'd expect it is just the coral growth leading to higher demand.

 

[tmz]

I stopped gfo in November. No change in calcium hydroxide dosing and no change in alk has occured; it's a steady 160 to 165ppm. I did boost the vodka. vinegar dose by 10% intially but have since backed that off ; PO4 remained low throughout.

 

[AcroporAddict]

Thanks, Jonathan, Randy, and Tom. I was hoping any or all of you would chime in.

Tom, I am hoping my system does like yours and the PO4 stays low without needing GFO use. Nice to have one less regular chore to do with the tank!

I have lowered the pH setpoint of my calcium reactor, so that should raise the alkalinity of the system. I'll test and adjust as needed. I added the kalk reactor maybe 14 months ago, and when I did I had to raise the setpoint of the ca rx because the KH went up to 11 with the added alkalinity from the kalk.

But I have had good growth from many of my Acro colonies, so I assume as the size of the colonies increases, then the demand for bicarbonates will as well, so this may be just a required adjustment of the reactor to the needs of the corals?

 

[bertoni]

I think that's correct. The corals likely are growing more as they get larger.

 

[AcroporAddict]

I think that's correct. The corals likely are growing more as they get larger.

Thanks Jon. I have 4-5 colonies a foot or more across now, and a bunch more at 8 inches or more across. Not every Acro I put in my 465 flourishes, but the ones that like it tend to do pretty well.

Also, I just tested KH again and it was at 8.3, so cranking down the ca reactor seems to have helped. I'll try to tweak it to a steady KH level over the next few days.