Post mortem on Deep Sand Bed

[tinyfish]

I do not know where else to post this.

I have had a 15g tank with 4" substrate (aragonite) and 15lbs. of live rock.
At first everything seemed to work OK. Bubbles were coming from the sand bed.
I had bristle worms and nassarius snails and added a neon goby.
Things looked OK over about 3 months then in the next 3 months I noticed black patches against the glass.

When I finally took the tank down this week, all the sand bed was black just below the surface, snails and worms were all dead and gone, but fish was OK.

I had a Koralia nano and a 20g power filter, 4x24w T5 lighting @ 6700k.

I think the sand bed suffocated and then died but I am not sure why it did that.

The purpose of the tank was to try sea grass. All the plants' roots rotted.

I have a deep sand bed in my display refugium. Display 75g, refugium 15g and I do not want the same thing to happen to this tank.

LFS said to poke sand bed with a stick monthly and do not stir.

Is there something else?

[3D-Reef]

Things looked OK over about 3 months then in the next 3 months I noticed black patches against the glass.

When I finally took the tank down this week, all the sand bed was black just below the surface, snails and worms were all dead and gone, but fish was OK.

I think the sand bed suffocated and then died but I am not sure why it did that.

The purpose of the tank was to try sea grass. All the plants' roots rotted.


The blackness is due too the lack of 02 and high DOC's.Increasing the flow will help with advection and also lower the DBL around the plants allowing more nutrient uptake.

[tinyfish]

I thank you for your post. I understand lack of oxygen creating the condition but I don't know what DOC's are or DBL. I am assuming it has something to do with the area around the plant's roots.

Also is there something besides flow to combat this? Besides the stick poking.

[Mavrk]

DOC = Disolved Organic Compounds

I don't know DBL, but I am guessing it is the build up of junk at a plants roots.

Flow is the best thing. Sand burrowing snails help too. Perhaps you needed more of those. But the point of a DSB is to have an anaerobic zone, so that is probably what you were seeing.

[3D-Reef]

DBL= Diffused Boundry Layer,a micro film of water that is void of nutrients that sticks to the plant leaf/rock/coral ect.The lower the flow and the more it's covered in epiphytic growth(i.e. bacteria,alga,debris,sediment particals),the thicker DBL is.On the flip side,high flow with low epiphytes results in a reduced DBL allowing for better nutrient up-take.

"Also is there something besides flow to combat this? Besides the stick poking."

There isn't a one time fix to the problem,but you can use things like a skimmer for the bigger organics and GAC for the smaller organics,water changes will also help.The best way is to limit the amount of organics in the substrate in the first place.

Did You use sand from an established bed when you set this up?If so,can You tell us about what % of used sand vs new sand, that you used?

[ruprecht]

Four inches of substrate seems a bit thick. One inch may have been more effective.

[sedor]

These days it doesn't make much sense to utilize a DSB IMO with all the nitrate fighting products available.

[TheH]

DSB would still be the best approach for sea-grass. Are you saying that in 6 months the entire sand bed (just below the surface) became black? How much food are you adding to this tank?

[tinyfish]

I only had a neon goby in this tank fed a tiny pinch every two days so feeding of food was not very much.

I failed to put in my original post that 50% of the substrate was taken from an existing setup that was over a year old, and it was allowed to cycle for 4 months prior to planting the shoal grass.

I can safely say that 1" is not enough on its own. Perhaps with supplementation. Personally I think 4" sounds like too much, but that is what is recommended by the sea grass supplier.

Yes, the sand bed turned black in that time 6 months. It seems that although the anaerobic layer is supposed to develop, it is not supposed to be the entire sand bed. I know my experiments in the past, again lead me to the lack of oxygen in the bed, however puzzling though because the water sustained fish and the water tests were always within parameters.

I read now that DOC's are desirable and the DBL is not.

It seems strange that I was supposed to add nitrate for the grass when it seems that there was too much nitrification going on in the sand bed. But I never saw the nitrates raise beyond 20. Perhaps I should have added the fertilizer when the nitrates were <10.

I did NOT have a skimmer on this setup thinking to increase the DOC's but I think in hindsight I should have used one.

I did do water changes of 1 gallon/week.

[mrrogers]

I would have used a skimmer for sure.

[3D-Reef]

I only had a neon goby in this tank fed a tiny pinch every two days so feeding of food was not very much.

Not feeding enough Could have had something to do with it too!If there isn't enough N03 going into the substrate,the bacteria will use Sulfate instead.Causing the black sand.

I failed to put in my original post that 50% of the substrate was taken from an existing setup that was over a year old, and it was allowed to cycle for 4 months prior to planting the shoal grass


I can safely say that 1" is not enough on its own. Perhaps with supplementation. Personally I think 4" sounds like too much, but that is what is recommended by the sea grass supplier.

Yes, the sand bed turned black in that time 6 months. It seems that although the anaerobic layer is supposed to develop, it is not supposed to be the entire sand bed. I know my experiments in the past, again lead me to the lack of oxygen in the bed, however puzzling though because the water sustained fish and the water tests were always within parameters.

I read now that DOC's are desirable and the DBL is not.

It seems strange that I was supposed to add nitrate for the grass when it seems that there was too much nitrification going on in the sand bed. But I never saw the nitrates raise beyond 20. Perhaps I should have added the fertilizer when the nitrates were <10.

I did NOT have a skimmer on this setup thinking to increase the DOC's but I think in hindsight I should have used one.

I did do water changes of 1 gallon/week.

I set up a 29g seahorse tank a little over a year ago.So I figured at the same time I would throw a grass tank together.I use ~30% "used" sand.What happened was that the turtle grass didn't make (sh tank is too cold),and the shoal grass is doing fine.But I had to fight cyano for the first six to eight months.Thank the Man up-stairs that's over!
I have since read that in the ocean,seagrass sediment,with a 0.5% organic load is on the low side and 2.6% is just this side of eutrophication.So I should have used a cup,maybe,two cups of sand instead of 16.:hmm5:

For shoal grass 2" would have worked,that's about how deep Mine is,but 4" is even better.

[outy]

this is easy, the black is from to much junk in the water plain and simple

10-20 is bad and very hard on the DSB

first it takes a long time to build up enough denitrifying bacteria to lower nitrates plus the surface area of the sand in a tank that small makes it very hard to be effective.

4" will work fine but you need to keep the water much cleaner

[GACDIVER]

Foot print is also in question. How small can you go and still have a viable and healthy meiofauna poupulation?

[EdSnyder]

I dont think this had anything to do with your water quality. I just went through this same thing. Mine problem started when a mis aimed pump blew a ton of sand into the corner of my tank. It buried a little calurpa I had in there. It died. The whole area turned black under the surface of the sand. In another part of the tank the sand piled up where there wasent any plants and I didnt have an issue.
My guess is the plants died for whatever reason and the roots rotted. This can happen very quickly. I had to get all the sand out of that whole area. Now everything is fine, half my tank has a deep sandbed and the other half is bare.

[Amp2020]

I've seen this happen in many tanks that I've taken care of. I don't have a scientific explanation but here's what I've seen. On tanks that used regular tap water for topping off, there seemed to be a higher likelyhood that the sand bed would turn black just below the surface. Once I started taking care of the tank and only used RO/DI water. The problem started to go away. One other tanks, the sand bed had to be changed. The owner bought the sand from a hardware store and thought that since it came from the beach that it was ok to use in his aquarium. But even at some beaches, this can be seen if you dig deep enough at the shore. Once the sand bed was replace with quality reef sand, we never saw any black spots.

I don't think that poking the sand bed is going to work very well. As soon as the sand bed uses up all of its oxygen, its going to start turning black very quickly. I've even tried using a gravel vacuum once a week and it still looked like someone dumped a bucket of activated carbon into the display tank. But in two days, the top layer turned back to white every time. I've never seen this happen with course gravel, like crushed coral. Only with sugar size sand or finer. So if you increase your flow, then I'd be willing to bet that you will have a hard time keeping it from being blown around in the tank.

[tinyfish]

Thank you all for posting.

To experiment I decided to take the black stinky sand and see what would happen if I used it again. I did rinse it but only twice so brand new RODI water was colored.

I set up two tanks. Both now have skimmers. Both 20g.
In Tank 1, I decided that I would try 1" of Eco's Miracle Mud and 3-4in. of the old sand.
In Tank 2, I just dusted the bottom of the tank but have 2" in a HOB refugium.

After 1 day:
Tank 1 smelled much cleaner and water was tan colored.
Tank 2 dark grey and still smelled.

Day 5
Tank 1 is clear and has diatoms on the sand
Tank 2 is clear

It seems that the organics in the Miracle Mud did make some difference in Tank 1.
It also seems that since both tanks have increased flow that difference may have also helped.
It may have also helped to have skimmers on both.

[spamreefnew]

any updates on the experiment? i have always wanted to do side by side tanks,one with miri mud and one with a skimmer just to put an end to the debate in my mind.

[jhnnle]

I had similar black patches in my DSB, but to only a mild extent. I changed over to the Jaubert/plenum system after doing some research, and have not had this problem since. My SPS are doing well so far.

[tinyfish]

I just read about the Jaubert/plenum system. Very interesting read.

I think I will set up a second tank with this system and compare to the first tank.

Update on Tank 1 with mud is that there were higher readings on some of the important parameters. I have to find my notes to post exactly what those were.

[davocean]

These days it doesn't make much sense to utilize a DSB IMO with all the nitrate fighting products available.

Some of us have creatures that require a DSB.
I've never heard of the poke it w/ a stick method!LOL
IMO 4" just begins to be an effective DSB, I prefer 5-6", and untouched other than surface vac lightly.
And if you don't want or need DSB 1" or less vac'd
M Mudd varies too much for me, not a fan of it, I've had algae issues come from it.

[joncd]

For a 20g like the OPs configuration would Miracle Mud (or a similar such product) be appropriate where a DSB may not?

[3D-Reef]

For a 20g like the OPs configuration would Miracle Mud (or a similar such product) be appropriate where a DSB may not?

The OP's original goal was to grow seagrass.The problem is in setting up the sediment so that DOC's are low enough that autotrophic denitrification bacteria dominate over that of hetrotrophic denitrifiers.
Seagrasses can and do grow in muds,silts,and sand,but,in araggonite only sediments,the grass is P limited.
In mud only sediments(or >25%) they become N limited,as the bacteria out compete the grass for ammonium.
So a mixture of both,mud and araggonite,is needed for lush growth.

[goodreef]

I failed to put in my original post that 50% of the substrate was taken from an existing setup that was over a year old, and it was allowed to cycle for 4 months prior to planting the shoal grass.



Here's your problem!! I know cause it happened to me too.

Your "old" substrate is full of detritus and nutrients. It should ONLY be used to top up the top 1 inch level.

Imagine. In your "old" setup, the oxygen level is properly distributed from the top to the bottom. Once you move it, all of the sand is exposed to high oxygen levels. Also, however much you clean the "old" sand, it never seem to be clean.

So, basically, if you use 50%, even just for the top, your old sand is at least 2 inches deep. At this level, before your sandbed is fully established, the detritus in the "old" sand starts to decay. The decay will quicky use up oxygen ... Thus, over few weeks, all the oxygen gets depleted, and Hydrogen Sulphite (black stuff) forms.

To avoid this in the future, do not add more than 1 inch of "old" sand to your new tank.

HTH

[bdbyace28]

That was definately a lot of sand for such a small tank. That is very possible that the depth created a lack of water flow and subsequent lack of oxygen. Good luck with your next tank