Sand Hardening (Calcium Carbonate Precipitation) with 2-Part Dosing and CO2 Scrubber

[Trenton Henderson]

Hey everyone! I posted somewhat recently on this forum about having issues with large dosing quantities and precipitation. The verdict was that it came down to testing.

I have a 60 gallon tank (75ish gallon system) where I dose BRS two part to aid in rapid coralline growth. The tank is 3 and a half months old and has no corals, three fish, a strawberry conch, and a skunk cleaner shrimp (with some trochus snails).

I started using a CO2 scrubber because my condo doesn’t get much fresh air. My pH stays around 7.8-8.0 (which isn’t terrible, but I wanted to get it a bit higher). After adding the CO2 scrubber, my pH sat perfectly between 8.2 and 8.4 all day.

After I began dosing, I couldn’t keep my alkalinity up to save my life. It would drop a lot no matter what I dosed. I got a dosing pump and dosed it to a high flow area of the sump (directly into a power head pointed at my return pump). I dose 24 times a day, and each part is dosed 5 minutes apart. I wanted to see if it was how fast I was dosing. This did not help.

I doubled the dosing quantity, just to keep it stable, but my sand began to turn into a brick! Recall that my tank is really young with a low bioload, and even though I used live sand, I believe the organics within the sand currently do not out compete surface area for abiotic calcium carbonate precipitation.

I tried everything except detaching my CO2 scrubber because I wanted to maintain a higher pH. Having no other option (even after stopping dosing for a few days), I removed the CO2 scrubber.

And behold! Rising and stable alkalinity and calcium! And because I dose soda ash (sodium carbonate), I get a little pH boost, so it’s not quite as low. My pH sits about 7.9-8.0 without it now, but it seems that abiotic precipitation is avoided.

Has anyone else dealt with this issue (CO2 scrubber causing precipitation in the sand)? How long did it take your tank to get to the point that you could raise the pH again without causing sand hardening, or did that ever happen?

I wanted to note that I did try using sodium bicarbonate instead, but I still had precipitation issues at a pH of 8.3. I would love to have my pH of 8.3 and an alkalinity level of 9 dKH, but if I have to settle for a pH of 7.9-8.0 to achieve that alkalinity, I suppose I will! Also, I am sure as I stock the tank more and dirty the sand with some organics, this may subside, but I could be wrong!

 

[Spare time]

If you don't have anything using the alk and calcium then why dose 2 part? Usually precipitation occurs when you dose too fast or in an area without high flow to quikly disperse it. What is the alk and calcium at right now?

 

[DrMMI]

I had this exact same issue recently. Randy recommended raising Mg, stop trying to boost pH, switch to sodium bicarbonate, and elevate organics. I followed his advice and my sand bed loosened up and my alk is finally stable. I just recently switched back to soda ash. I'm still dosing a lot more than I used to, but at least the dose is stable.

 

[stevolough]

It also is caused by dosing more then you need.

 

[Spare time]

I have a cave made of hardened sand in my tank from when I had this issue haha

 

[Trenton Henderson]

@ Spare time:
I originally started dosing two part because my Alk was consistently dropping. I believe this started out by the nitrogen cycle in my tank, but even with a stable bio load, it continues to drop (notably when my pH is 8.2-8.4), though I have a bit (not a ton) of coralline growth taking off. My Alk is about 7-7.3 dKH this morning, which is trending down by about 0.5 dKH per day (or a little under) while dosing 40 ml/day of BRS Soda Ash over the course of 24 hours. Calcium hangs about 400 ppm, with the same 40 ml/day dosing; I wanted to see if I could stabilize Alk before raising calcium again because it seemed pretty stable at about 400 ppm.

@ DrMMI:
My Mag is about 1350-1400 most of the time, so that isn't an issue. I have tried increasing my feedings to increase organics. And pH is the only thing that seems to consistently work for my tank. When the pH drops to 7.8-8.0, my Alk consumption is decreased. The second I raise it, the Alk consumption increases. I use Sodium Bicarbonate when I want to do a larger correction adjustment. Have you been able to elevate your pH?

@ stevolough:
I'm wondering if my true Alk consumption is incredibly low. Maybe I should shut off my dosing pump for the day and see what happens tomorrow morning. If the numbers don't decrease all that much, there is my answer. What do you think?

 

[DrMMI]

@ Spare time:
I originally started dosing two part because my Alk was consistently dropping. I believe this started out by the nitrogen cycle in my tank, but even with a stable bio load, it continues to drop (notably when my pH is 8.2-8.4), though I have a bit (not a ton) of coralline growth taking off. My Alk is about 7-7.3 dKH this morning, which is trending down by about 0.5 dKH per day (or a little under) while dosing 40 ml/day of BRS Soda Ash over the course of 24 hours. Calcium hangs about 400 ppm, with the same 40 ml/day dosing; I wanted to see if I could stabilize Alk before raising calcium again because it seemed pretty stable at about 400 ppm.

@ DrMMI:
My Mag is about 1350-1400 most of the time, so that isn't an issue. I have tried increasing my feedings to increase organics. And pH is the only thing that seems to consistently work for my tank. When the pH drops to 7.8-8.0, my Alk consumption is decreased. The second I raise it, the Alk consumption increases. I use Sodium Bicarbonate when I want to do a larger correction adjustment. Have you been able to elevate your pH?

@ stevolough:
I'm wondering if my true Alk consumption is incredibly low. Maybe I should shut off my dosing pump for the day and see what happens tomorrow morning. If the numbers don't decrease all that much, there is my answer. What do you think?

I switched to sodium bicarbonate for about 2 weeks until I got my alk stable where I wanted it. pH took a little bit of a hit for a while. Once everything was consistently stable for about 2 weeks, I switched back to soda ash and so far it's been holding up. Here's a link to my original post

Cannot keep Alk up

I apologize ahead of time for the long post, but I wanted to make sure I didn't miss anything. I recently moved this past July into a bigger home. I have a 260g mixed reef with mostly LPS. Prior to the move, I was dosing about 200ml a day of Ca and sodium hydroxide (needed the pH boost) and alk...

www.reef2reef.com

 

[stevolough]

Stopping dosing for a few days and checking your actual consumption is definitely a good plan. I’ve never used a co scrubber so I have no input on that. I have a 100 gallon tank with a couple dozen lps and Zoas and I only dose 8ml of two part a day. There was a time I was dosing 40 ml a day. All my tests were in range so I kept dosing and ended up with a sand bed of stone. Randy and others do a great job of explaining it. Do a search on precipitation. If you’re like me you’ll have to read the posts an articles few times!

 

[Trenton Henderson]

So I’m going to try a couple things, and I will keep everyone posted.

First, I’m going to stop dosing for the next couple days and see if my alkalinity levels off or decreases at a slower rate. I’ll adjust accordingly from there with Sodium Bicarbonate to get it to my desired level of 9 dKH.

Second, in the instance that the first method doesn’t work, I will remove my CO2 scrubber again and repeat the first method again.

I’m interested to see if there is a repeatable method of stopping this from occurring.

Also, as an aside, my sand does not seem to be taking the brunt of the precipitation anymore due to more organics and the advent of a bit of diatoms, so we shall see! But again, I’ll keep you all posted. If anyone else has pointers, especially if you have a CO2 scrubber, I’d love to hear the input!

 

[Randy Holmes-Farley]

Once a calcium carbonate precipitation event is initiated (due to high alk and pH, for example), you need to break the cycle because the surfaces of any precipitate act as good seed crystals for more precipitation until soemthing gets onto those surfaces and blocks further precipitation.

Here's my generic advice for such scenarios:

1. Stop all efforts to boost pH.
2. Stop dosing alk for a bit and let it decline.
3. Reduce pH by switching to a low pH alk mix like sodium bicarbonate, or a calcium organic such as Tropic Marin All for Reef.
4. Ensure magnesium is normal to high.
5. Keep organics and phosphate on the high side.

After a few days of not dosing alk, restart slowly, adding additives to a very high flow area so it mixes in fast.

 

[Trenton Henderson]

Once a calcium carbonate precipitation event is initiated (due to high alk and pH, for example), you need to break the cycle because the surfaces of any precipitate act as good seed crystals for more precipitation until soemthing gets onto those surfaces and blocks further precipitation.

Here's my generic advice for such scenarios:

1. Stop all efforts to boost pH.
2. Stop dosing alk for a bit and let it decline.
3. Reduce pH by switching to a low pH alk mix like sodium bicarbonate, or a calcium organic such as Tropic Marin All for Reef.
4. Ensure magnesium is normal to high.
5. Keep organics and phosphate on the high side.

After a few days of not dosing alk, restart slowly, adding additives to a very high flow area so it mixes in fast.

I have taken my CO2 scrubber off line and successfully maintained the Alkalinity I wanted for a week, but when I turned it back on, after 24 hours, it had dropped. Any idea as to why a pH change from 7.9-8.0 to 8.2-8.4 immediately seemed to precipitate Alkalinity?

Currently, I still have my CO2 scrubber connected, but have stopped dosing, and I am still seeing a declining Alkalinity, so it seems to still be an issue surrounding the pH. I have tried dosing Sodium Bicarbonate with the same results as Sodium Carbonate.

I would like to maintain my pH at 8.3, and many do with even higher levels of Alkalinity, so I’m not entirely sure why my case is different.

Also, you say I can begin dosing Alkalinity slowly until it stabilizes, but when could I raise my pH back up again?

Any thoughts?

 

[Randy Holmes-Farley]

I have taken my CO2 scrubber off line and successfully maintained the Alkalinity I wanted for a week, but when I turned it back on, after 24 hours, it had dropped. Any idea as to why a pH change from 7.9-8.0 to 8.2-8.4 immediately seemed to precipitate Alkalinity?

Sure. Precipitation is very sensitive to pH, as is other types of consumption.

 

[Trenton Henderson]

Sure. Precipitation is very sensitive to pH, as is other types of consumption.

Will there be a time where I will be able to bring my pH back up, or will I have to live with a lower pH?

 

[Randy Holmes-Farley]

Will there be a time where I will be able to bring my pH back up, or will I have to live with a lower pH?

Hard to say, but generally, the idea is to let the bare calcium carbonate surfaces get coated with stuff that prevents further precipitation before raising alk and pH.

 

[Trenton Henderson]

Hard to say, but generally, the idea is to let the bare calcium carbonate surfaces get coated with stuff that prevents further precipitation before raising alk and pH.

I have very few inhabitants yet (young tank), so perhaps with more fish and time, the tank will be prepared for a higher pH due to a greater coating of organics, would you say?

 

[Randy Holmes-Farley]

I have very few inhabitants yet (young tank), so perhaps with more fish and time, the tank will be prepared for a higher pH due to a greater coating of organics, would you say?

new tanks are particularly susceptible to sand hardening, like due to less stuff coating it.

 

[Trenton Henderson]

new tanks are particularly susceptible to sand hardening, like due to less stuff coating it.

Thanks for all the help. I’ll just keep that CO2 scrubber off and test it occasionally until I am able to maintain that pH.