2 part precipitation

Fishfinder · Jun 17, 2017

I'm weak in my chemistry skills. I know if you dose too much calcium with low mag it will precipitate. But dosing too much alk can't cause precipitation can it?

Randy Holmes-Farley · Jun 17, 2017

Definitely it can. Raising alk from 7 to 14 dKH (even with no pH rise) has the same effect on precipitation as raising calcium from 420 to 840 ppm.

Also, raisng the pH from 7.8 to 8.1 has about the same effect as the above boosts, so pH is a huge driver.

Fishfinder · Jun 17, 2017

So adding alkalinity portion that raises ph (like soda ash) can cause precipitation? Would that only occur if mag is low?

I need a good chemistry lesson. I need to find a dumbed down article

Randy Holmes-Farley · Jun 17, 2017

Fishfinder said:
So adding alkalinity portion that raises ph (like soda ash) can cause precipitation? Would that only occur if mag is low?

I need a good chemistry lesson. I need to find a dumbed down article

Most reef aquaria have some precipitation, such as on warm objects like heaters and pumps. Magnesium is, IMO, only a minor player and you should be maintaining it anyway if low High pH and high alk are the biggest drivers of precipitation in a normal reef tank. So yes, a high pH alk supplement contributes.

Fishfinder · Jun 17, 2017

I was under the impression that high mag would prevent precipitation?

Randy Holmes-Farley · Jun 17, 2017

Fishfinder said:
I was under the impression that high mag would prevent precipitation?

Magnesium at any concentration reduces the rate of precipitation, and the more you have the bigger the effect, but no, it cannot stop precipitation if there's a big enough driving force.