Sand bed leaching alkalinity?

[Nick Steele]

Tank status
Nuvo 20
2 ai 16hds
2 jebao sow4
South seas caribsea rock
Carina sea specia grade sand
2 clowns
7 hermits
5 trochus snails

I’ve always had some issues with weird increase in alk. I would get a small drop over the course of one week do a water change (turkey baste the sand and rock) and over the next few days I would get a .5-1.5 dkh rise in alk. I did have a bad batch of salt that would mix at 8-12 dkh that I have since gotten rid of and new salt will mix at 8.4 every time now. I had my alk at 8.8 a few weeks ago but is now at 9.8 again. Also I do use rodi unit to make my water at 0tds.

Is it possible that my sand bed could be leaching alkalinity?

If so would it be detrimental to remove the old sand bed and leave it bare bottom for a little while then add new sand back in?

 

[xxkenny90xx]

What kinds of corals do you have in the tank? Removing the sand is fine but I'm not sure I see the point if your just gonna put new sand in??

 

[Randy Holmes-Farley Verified Community Expert]

Tank status
Nuvo 20
2 ai 16hds
2 jebao sow4
South seas caribsea rock
Carina sea specia grade sand
2 clowns
7 hermits
5 trochus snails

I’ve always had some issues with weird increase in alk. I would get a small drop over the course of one week do a water change (turkey baste the sand and rock) and over the next few days I would get a .5-1.5 dkh rise in alk. I did have a bad batch of salt that would mix at 8-12 dkh that I have since gotten rid of and new salt will mix at 8.4 every time now. I had my alk at 8.8 a few weeks ago but is now at 9.8 again. Also I do use rodi unit to make my water at 0tds.

Is it possible that my sand bed could be leaching alkalinity?

If so would it be detrimental to remove the old sand bed and leave it bare bottom for a little while then add new sand back in?

Sand beds very slowly dissolving is real, but rarely any problem since it is far lower than the demand in most tanks, and it won't happen at uneven rates like you suggest. Just a slow steady dissolution. Live rock likely does too.

 

[Nick Steele]

Sand beds very slowly dissolving is real, but rarely any problem since it is far lower than the demand in most tanks, and it won't happen at uneven rates like you suggest. Just a slow steady dissolution. Live rock likely does too.

Okay thanks! Guess I won’t go and rip my sand bed out quite yet then.

 

[Dan_P]

Sand beds very slowly dissolving is real, but rarely any problem since it is far lower than the demand in most tanks, and it won't happen at uneven rates like you suggest. Just a slow steady dissolution. Live rock likely does too.

What is the rate of dissolution? 1% per year? 0.1%?

 

[GlassMunky]

Yes that can happen. Here’s another thread where it goes into details

Alkalinity rising without dosing... possible causes?

Over the past month or 2 I've been experiencing the very strange phenomenon of my alk rising without me dosing it. I have a theory as to why that I'd like to run past you all. I reintroduced a decent amount of sand that had been siphoned out of my tank from a while back, that was stored damp...

www.reef2reef.com

 

[GlassMunky]

What is the rate of dissolution? 1% per year? 0.1%?

My tank was raising by 0.1-0.2dKh per day... 210G tank with 65g sump.

I’ve since gone through and manually cleaned the sand and the following day the ALK raise stopped....

I can’t think that’s a coincidence....

 

[Randy Holmes-Farley Verified Community Expert]

What is the rate of dissolution? 1% per year? 0.1%?

Some experienced reefers with long term tanks (e.g., Larry Jackson) added his sand back every few years, so in his tank it seems like 5%? Something on that order of magnitude. May vary a lot with sand surface area, water flow, deteritus accumulation in the sand, etc.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, sand can also potentially dissolve inside the GI tract of animals where the pH may be lower. Fish, sea cucumbers, etc.

 

[Nano sapiens]

In the 12+ years of running my small system I've replaced about 5-10% of the aragonite substrate (Kalkwasser used exclusively).

I've been seeing a few threads lately regarding this issue of either stalled or rising alk with no intentional external means of supplementation. I just had a similar experience where I was attempting to let alkalinity drop from 12.5 dKh (faulty test kit) to 9 dKh by reducing KW usage in my ATO. As I steadily reduced KW over a few days, I noticed that alk was dropping much more slowly than expected and when I stopped KW completely the system stayed at 10.5 dKh for nearly a week with only RO for topoff. Complicating matters, I had also reduced lighting intensity by about 7% during this period to reduce stress on a few SPS corals that had suffered due to the higher alk.

A thorough cleaning of the sand bed, a 20% WC for the week and opening windows to get some fresh air for a short period each day in the house and the alk dropped much more quickly over a day or two to my intended 9 dKh. Consequently, I had to start KW again to maintain the current level.

I've had similar lowered KW usage events happen many times over the last 12 years, but never as extreme as this year. And interestingly, these events have typically occurred at the end of autumn/beginning of winter.

 

[Dan_P]

Some experienced reefers with long term tanks (e.g., Larry Jackson) added his sand back every few years, so in his tank it seems like 5%? Something on that order of magnitude. May vary a lot with sand surface area, water flow, deteritus accumulation in the sand, etc.

Not sure anyone would notice a 5% loss of sand.

Let’s assume aragonite sand dissolves. To calculate a daily alkalinity increase, let’s assume we have an aquarium with 1.45 lb sand per gallon. What daily alkalinity increase would we see for various annual percent sand bed dissolution rates? Check out the plot below.

The notion of a dissolving sand bed might have merit. It is still only supported by anecdotal evidence, but an idea worth looking into.

 

[Simbol]

So is there any Sand we can use in Reef Marine that would not leach Alk?

 

[Dan_P]

So is there any Sand we can use in Reef Marine that would not leach Alk?

I am not aware of any such sand, though I never read where it is a problem.

 

[Simbol]

though I never read where it is a problem.

On this thread? and here: https://www.reef2reef.com/threads/alkalinity-rising-without-dosing-possible-causes.731986/page-4

I am suffering from this with a tank that is only 8 months old.. I have been going nuts..

S.

 

[Dan_P]

On this thread? and here: https://www.reef2reef.com/threads/alkalinity-rising-without-dosing-possible-causes.731986/page-4

I am suffering from this with a tank that is only 8 months old.. I have been going nuts..

S.

O, sorry! Obviously I need to pay better attention.

If you were to remove a sample of sand from your system and place it a sample of aquarium water, aerating the water if practical, would this sample water alkalinity increase like it does in the aquarium? I am looking for ways we can prove it is the sand.

 

[Randy Holmes-Farley Verified Community Expert]

So is there any Sand we can use in Reef Marine that would not leach Alk?

If calcium carbonate sand is slowly dissolving, then silica sand will prevent that issue.

 

[Simbol]

If calcium carbonate sand is slowly dissolving, then silica sand will prevent that issue.

Hi Randy,

Thanks for the response, is it safe to use silica sand in reef aquariums then?

S.

 

[Randy Holmes-Farley Verified Community Expert]

Hi Randy,

Thanks for the response, is it safe to use silica sand in reef aquariums then?

S.

Some release of silicate will happen, but generally not a problematic level. I’d use a natural sand, which is naturally well washed, not ground up stuff like for sand blasting.

 

[Simbol]

Hi Randy Thanks, I performed an experiment and:

1) Cleaned my coarse aragonite sand.
2) Increased flow of the tank by 30-40%
3) Dropped my Gyres about 7 cm closed to the sand bed to increase flow around it.
4) Increased aeration in the living roon to raise PH.

These combined gave me Alk drop for the first time.. so clearly the issue is low PH zones in the sand bed.. my automatic KH tester (KH keeper, it test every 2 hours) is confirming my Alk raises between 4am to 12pm when my tank PH is below 8.1. I am now looking now to install a CO2 scrubber to keep PH higher and improve the situation.

I want to thank everyone for all the imput on these forums, it really helped me to understand the cause of the issue and how to attack the symptons to improve the situation!

Regards,
Raul from UK