Does Controlled Phosphate Leaching from Live Rock Hurt SPS Corals?

[Randy Holmes-Farley Verified Community Expert]

I have to believe that the PO4 is my issue, and I've read time and again that rock leaches PO4, sometime for a very, very long time. But if I'm keeping PO4 at a steady rate of 0.05ppm, would the PO4 leaching from my rock still have an adverse impact on my corals?

Steady release from rock is no different to a coral out in the water than is the large steady addition from foods.

 

[Randy Holmes-Farley Verified Community Expert]

@Clownfishy that's a bummer but unfortunately I've read the same thing many times - that some rock can have PO4 leech (or as @jda puts it - "unbind") for years. I'm just wondering if there is any indication that the leeching could hurt SPS corals so long as the PO4 is left in check.

I, too, have considered buying new rock, removing all the PO4 in a bin, and then changing out my current rock with that. Only problem is I'm concerned that all the good bacteria, etc that is in my current rock is beneficial, and removing that could be detrimental in and of itself.

I do not believe the "years" comment.

Equilibration of exposed phosphate between tank water and exposed surfaces will happen in hours to maybe a few days. Of course, if you keep trying to lower it again and again, it will need to equilibrate each time.

Phosphate down in rock pores will leach out and reach equilibrium far more slowly, but that source becomes less and less impactful simply because it is coming out more and more slowly until it is totally lost in the huge amount of phosphate added each day in foods.

 

[sgrosenb]

That's great info - thanks @Randy Holmes-Farley and @Dennis Cartier and @Dburr1014. It sounds like it's highly probable that PO4 is not my issue, or that it could be too low and the increase is due more-so to my food as @MnFish1 suggested rather than rock leaching. Now if I could only figure out what is stunting my coral growth.... I'll try upping my PO4 to 0.1 and lower my water change amounts to 10% weekly.

 

[jda]

The aragonite will unbind. Whether or not it is an issue has more to do with what the residual level is. All rock and sand likely have some. Mine do - they keep the tank about about .005 to .01 ppm of phosphate. This is no issue.

Cutting back on feeding is no way to fix this. This will starve the coral of available nitrogen which can probably cause more issues with growth than having .05 ppm of residual phosphate, which most find no issue with.

The idea is to up the export, not cut the import.

FWIW - residual po4 levels of 1-3 ppb is not limiting in anyway way, so raising from .05 to .10 will not likely do anything unless it was increased feeding that gets people there in which case the increased feeding is what mattered and not that the residual po4 level rose.

It is probably minor, but the phosphate unbinds - it does not leach (or even leech). Unbinding is different and requires a suitable environment to happen. It also means that it can bind more, to those who understand the difference. If you do raise your tank po4 level to .10, the rock and sand will bind more phosphate when you do. People have misunderstood the term leach before and thought that all of the phosphate would just wash away and not that it had a permanent relationship with the water column.

I do know of many cases where it took years and gallons and gallons of GFO to get all the po4 out of rock. Even though the release can be quick for aragonite structure near the surface, you do not want to remove it too quickly in a real reef tank. You can go much faster if you isolate the aragonite in separate container.

 

[MnFish1]

Thanks all. To be clear - my lights are on for a total of 12 hours - 3 hours ramp up, 6 hours full blast, then 3 hours ramp down.

I'm still curious if anyone has more insight into whether rocks releasing PO4 is detrimental to corals if the PO4 is ultimately kept steady at a level of roughly 0.05ppm.

Sorry - I thought I answered that - If the level is continuously at 0.05 - the leaching (or as one person called it 'unbinding') will not cause a problem. The key is - are your tests correct - and are you monitoring day to day - and different times of the day - to be sure the Phos is not higher at some points.

As @Dennis Cartier said - your 0.05 may be lower. (or higher)