can low ph "unbind" phosphate?

joshuajoshua · Sep 22, 2014

I recently added some rock that came from a poorly maintained tank. Prior to putting the rock in my tank I gave it a muriatic acid bath, pressure washed, and soaked in rodi for about 2.5 weeks.

Since then I have been having a bit of an algae outbreak. I figured it's just part of the uglies since I added more rock. But, I have noticed fairly high phosphates, like .18 to .24, but I quickly changed out the GFO and am lowering it as we speak.

So i am not sure if this phosphate is from the rock, but I'm pretty sure it is. I think it could be decay causing it, but is it possible that my low ph 7.85-8.05 could be causing the rock to leech phosphate back into my tank? And if so, how long will this continue?

Thank you very much

Randy Holmes-Farley · Sep 22, 2014

Well, muriatic acid would have removed most surface phosphate.

The pH of the water won't have a huge effect on the release of additional phosphate within the range we normally see in a reef tank, but it has some.

If there is decaying organic matter on the rock, that can release additional phosphate, and if there is phosphate throughout the rock, some may slowly leach out over time.

IMO, you've done a reasonable job of cleaning it and I'd just keep treating the water in the aquarium.

All foods also keep adding substantial phosphate, and you need export for that reason even with no rock present.