What’s causing the precipitation

[Ziggy17]

Folks all the chem lovers, I pose a question. What is causing the precipitation in the tank?

Background.

I decided to mix up and dose DIY snow using calcium bicarbonate as per a thread on R2R. I wanted to try it out and see if the water could in fact get more clear. Dosed 7ml into a75g. Everything cleared up in about 6 hours and things seemed normal. Next day I ran a comb8ned test on the trident. Calcium reading went through the roof. From 420 to 505. Posted a thread. Randy suggested the food grade bicarbonate likely had some contamination that was causing a false reading. No precipitation though. Fast forward a week. Same dose, same result. However a day or two after the second dose, the tank started to precipitate. Trident was reading north of 500 again, but mag also shot up to 1500 and my alk to 10.8 from a steady 8.9-9.1. I tested my alk with my Hanna and kept getting in the 9 range. I figured something knocked out the calibration on the trident, but I shut down my AFR dosing head until I knew where my calcium actually was. PH has been sitting around 8 the whole time. Via both my apex and my Hanna hand held. Salinity was a steady 35ppt. I decided to do a 12.5% WC to see what that changed. Calcium reading was 280. Clearly a trident issue. Got a Salifert calcium test kit. Reads 400. Right on track to what the depletion of my calcium would be after a few days of not dosing. Mag. I’m Salifert reads 1400, again, tracking where it was prior to the trident hiccup.

Today when I woke up the precipitation was nearly gone. The dust wasn’t built up on the rockwork like it had been. So that’s all positive.

But still wondering what was causing the precipitation in the tank if PH was 8 and calcium never about 420…?

Thanks in advance for your time.

Edit. The water didn’t get any clearer FTR haha

Zig.

 

[Miami Reef]

I’m a bit confused because you mentioned calcium bicarbonate.

Did you mean calcium carbonate?

I’m not sure what happened with the testing, but adding calcium carbonate powder will not cause alk, ca, nor mag to increase. It’s completely insoluble at seawater’s natural pH.

You said there was precipitation? Can you expand on that part? Was it just the CaCO3 powder that settled on the rockwork?

 

[Miami Reef]

Adding calcium carbonate has the potential to increase the likelihood of precipitation. It adds freshly exposed calcium carbonate surfaces which can act as seed crystals to encourage precipitation.

However, I doubt this is significantly happening in an established tank with normal alk and pH around 8.

 

[Ziggy17]

I’m a bit confused because you mentioned calcium bicarbonate.

Did you mean calcium carbonate?

I’m not sure what happened with the testing, but adding calcium carbonate powder will not cause alk, ca, nor mag to increase. It’s completely insoluble at seawater’s natural pH.

You said there was precipitation? Can you expand on that part? Was it just the CaCO3 powder that settled on the rockwork?

Yep calcium CARBONATE. My autocorrect loves the word bicarbonate. Probably from my DIY alk questions.

it was like light snow flurries in the tank. But more than a day after it had cleared up. So I didn’t think it was settled powder remaining from the dose getting stirred up, But I guess that really all it could be if nothing chemically can cause that to happen.

 

[Miami Reef]

Do you have sand sifting gobies by any chance?

 

[Ziggy17]

Do you have sand sifting gobies by any chance?

I do. But I got so lucky with him. He stays on the sand. He doesn’t carry the sand up in the water column. But I’m sure there’s times he does that. I also have a Malanurus wrasse that dives in at night.

Definitely potential culprits that I hadn’t thought of.

 

[Ziggy17]

Appreciate your time. I may blow the snot out of the rocks and sand to get more up and out so it’s not a constant flurry whenever something stirs the sand.

 

[Randy Holmes-Farley]

It’s very uncommon to get suspended calcium carbonate precipitation without some kind alk or pH spike event.

I’d just keep watching and see if it recurs, and under what circumstances.