I HAVE A CHEMISTRY QUESTION: adding Ca to precip ALK

BanjoBandito · Jun 28, 2022

So, I'm not gonna rehash what idiot moves I did yesterday but I'm sitting here with a pretttttttty high ALK (13.8) and I'm thinking if I dose a lil' calcium I can precip it out. My Ca is already at 475. Normally I like to be around 8.5 ALK but a rogue CO2 scrubber incident dosed straight PH/ALK slurry into my tank. I got the PH calmed down but my ALK is still high. Will this precip out naturally? Or should I dose Ca to precip it out?

Randy Holmes-Farley · Jun 28, 2022

Generally, calcium is a poor driver of precipitation or consumption. pH and alk itself are stronger drivers.

There’s nothing wrong with boosting calcium to 550 ppm, but that will only be a minor effect on the alk decline, and will leave high calcium once the alk is down.

mattdg · Jun 28, 2022

Even though you Cal is high, it is an appropriate level in comparison to your now high ALK. If you are not immediately worried about livestock, such as SPS in your tank, you can slowly lower the levels together with a few water changes and continue dosing when things level out. It is hard to offer advice, not knowing the age of your system and how much coral is growing in it. Generally, water changes are the solution, but in cases where you have a ton of coral mass, simply turning off your dosers, until the coral take up the additional Alk/Cal, may be the best solution.

ReefGeezer · Jun 28, 2022

I see by your build thread that you have some Acro frags. They may already be affected, but may be harmed more by another rapid change. I'd probably do water changes with water that had muriatic acid added to reduce its alkalinity. But... I'd do so slowly.

Randy Holmes-Farley · Jun 28, 2022

mattdg said:
Adding more cal is not the solution. It will simply continue to raise cal levels, until the Cal itself precipitates out of solution.

That sentence seems confusing to me. You do realize that to remove 20 ppm of calcium that way will drop alk by 2.8 dKH?
There is no other way to precipitate calcium in seawater then to form calcium carbonate.

BanjoBandito · Jun 28, 2022

Everything seems fine, I ended up doing about 50% of a full system water change yesterday to tackle the PH problem. My acros seem "fine". Corals seem "fine"....no color loss or changes? My clam is livin' it up...somehow....nothing is showing any real impact other than the cloudiness of my water. I might just do another 10-15% water change and let it burn out over time. I don't run an ULNS, so running higher might be OK for awhile me thinks....Also, for anyone wondering, high PH will make your urchins spawn. Proved that out.

Randy Holmes-Farley said:
That sentence seems confusing to me. You do realize that to remove 20 ppm of calcium that way will drop alk by 2.8 dKH?
There is no other way to precipitate calcium in seawater then to form calcium carbonate.

This is what I am asking kinda Randy....if I just juice the Ca over 500 and kinda "force" precipitation, am I doing something very dumb or very big wrinkle brain? Or is this something that works in theory better than in practice? Is this a situation where I've been given too much science?

Randy Holmes-Farley · Jun 28, 2022

BanjoBandito said:
Everything seems fine, I ended up doing about 50% of a full system water change yesterday to tackle the PH problem. My acros seem "fine". Corals seem "fine"....no color loss or changes? My clam is livin' it up...somehow....nothing is showing any real impact other than the cloudiness of my water. I might just do another 10-15% water change and let it burn out over time. I don't run an ULNS, so running higher might be OK for awhile me thinks....Also, for anyone wondering, high PH will make your urchins spawn. Proved that out.

This is what I am asking kinda Randy....if I just juice the Ca over 500 and kinda "force" precipitation, am I doing something very dumb or very big wrinkle brain? Or is this something that works in theory better than in practice? Is this a situation where I've been given too much science?

It isn’t going to force anything fast. A rise in calcium from 475 to 550 ppm calcium only gave the same driving force for precipitation as a 0.06 pH unit increase, or an alk rise from 8 to 9.3 dKH. As you can see, pH is the big driver for normal reef aquaria.