Phosban and Alk

[Scouter Steve]

I notice that when I replace my phosphate media my Alk drops off significantly. I dose to correct this. My question here is does the absorption of Alk make the phosphate media less capable of absorbing phosphate? And if I was running low Alk would the change be less significant.

 

[mps9506]

First time I used a ferrous oxide phosphate abosrobing media I noticed the same.
As I and many others learned the hard way, it is best to change a small amount at a time if you are using a large amount of it, and if your tank has never been on it before only add a little at a time.
Using a large amount of new media will rapidly alter the water chemistry and can/will stress the corals. I didn't use a reactor like most people I used several small bags in the sump without any major flow pointed at them or through them. Made it easy to change media on a regular basis a little at a time.

If it is having that much affect on your alk, and you are using a reactor, try using a smaller amount in your reactor and change it more frequently.

 

[Scouter Steve]

I see a drop in Alk when I change media now. Does that mean my media has been exhausted for some time already? I have been running 2 reactors for a couple months now and alternate refilling overlapping by 3 weeks. In other words I change one every 3 weeks.

 

[mps9506]

How much of a drop do you see? Do you do any phosphate testing (if you are running a macroalgae fuge this might not be worthwhile)?

 

[tbittner]

VERY interesting topic. I'm learning about this too. I didn't notice a drop in the Alk though but my alk runs a little high because I'm dosing the B-Ionic solution.

I run two reactors and they are both full but I've been running them for a while now.

 

[Scouter Steve]

I test phosphate, always been zero of course. I do run a fuge so yeah a useless test.
As far as drop it can go from 8.6 to 8.0 overnight. I dose daily with two part and always bump it up after a media change. My reactors are about 1/3 full. I am considering stopping the reactors altogether. My worst algae is a macro (Dycota sp?) very little hair.

 

[mps9506]

Feature Article

The pH in the tank with no Rowaphos dropped slightly over the 22 hours, from 8.19 to 8.09. As figures 3 and 4 show, pH dropped for both tanks with Rowaphos. The tank with elevated pH and alkalinity dropped the furthest, nearly one pH unit. In contrast, the tank with lower initial pH dropped only 0.2 units. The tank with alkalinity of 7 dKH at the beginning of the run was still 7 dKH at the end. In contrast, the tank with alkalinity of 16 dKH declined to 11 by the end of the run. While further study is necessary to draw definitive conclusions, the super-saturated state that some hobbyists operate their tanks may account for the problems reported. Regardless of the explanation, a hobbyist using iron oxide based phosphate removers should be aware of the potential decline of pH and plan accordingly.

Maintaining a higher alk won't really help prevent the drop. I would just add some alk supplement a few hours after you change your media if you want to keep running phosban/rowa.

 

[Scouter Steve]

WOW that article seems to have been written just to answer my question! Maybe I should just stop trying to get up to 10 dkh for my Alk.

Still wonder if when it drops the Alk if I have taken some of the effectivness away from the phosban.

 

[mps9506]

Still wonder if when it drops the Alk if I have taken some of the effectivness away from the phosban.

Does not look like it:
Iron Oxide Hydroxide (GFO) Phosphate Binders by Randy Holmes-Farley - Reefkeeping.com