appropriate substrate depth

[lmetcalf]

Hello all,
Im setting up a new FOWLR aquarium, 30gal. I've heard differing opinions regarding how deep my substrate should be.
The issue is regarding anaerobic bacteria and their usefulness. In my understanding (please correct me if i've got this wrong) they have the ability to utilize ammonia (I think, or some other bad chemical) and create inert nitrogen gas, and exist in deep substrate where oxygen is scarce. Unfortunetly they can produce trace ammounts of toxic stuff too. I read somewhere that they might not actually be able to metabolize ammonia in an aquarium because of the high concentration of oxygen.

This is a lot of information! So i don't know what to do. Im not using an undergravel filter. (just powerfilter and protein skimmer)
Should i have a 1/2 inch of substrate or 3 inches? or something inbetween??

Thank you for any and all input!!!!!

 

[match55]

hmm I have 1inch~1.5inches,
or you can go for a deep sea bed (DSB) 4~6inches. don't know if ppl do that in DT, usually see in refugium.

and yes, the bacteria break down ammonia to nitrite, then break down to nitrate.

if u have enough surface flow, there should be enough gas exchange at the surface and provide enough oxygen to the tank.

I will suggest 1.5~2 inches of sand, cuz you have live rocks too i assume, so there will be enough bacteria to break down the bad stuff in your tank. also save some money on sand, so you can get more fish hahah

 

[lmetcalf]

I understand that aerobic bacteria break down the ammonia into nitrate, (nitrogen cycle) but what about anaerobic? (ammonia into nitrogen gas)

Ive heard mixed opinions about whether anaerobic bacteria is ok (therefore go with deep substrate)

OR

Stop the growth of anaerobic bacteria and only have aerobic bacteria (shallow substrate)

Im not sure if this anaerobic bacteria sounds like a good thing.. is this the "bad bacteria" that everyone talks about?

 

[match55]

did a little research for you
I believe they r good and thats why some ppl have deep sea bed.
"Good deep sand (#00) beds of over 2” also are helpful as these allow anaerobic bacteria to form and off nitrates."

so they help take off nitrate which is good~ ^^

 

[melosu58]

How Sandbeds REALLY Work by Ronald L. Shimek, Ph.D. - Reefkeeping.com

 

[Zer0]

Melosu gave a great link, but im gonna throw some two cents in this one.

The depth of your sandbed is really going to depend on what kind of livestock you have. I know people that have bare bottom reefs where it's just the glass. Not many people, but there definitely are some. If you plan to have fish like some gobies that like to dig under the sand, you're going to need a sufficient depth for them to be able to achieve this. Usually 3 inches is a good depth. As for other things like snails that live in the sand(nassarius) or pistol shrimp that build their home/burrows in the sand, they also need a fairly deep sandbed. My sandbed depth is 2.5"s in some places and 3"s in other areas. As i said before, it really all depends on the livestock you plan on having. Dually note that if you have things like gobies or pistol shrimp, that make their homes under the sand, you're going to need to make sure that your live rock is placed firmly in the sand. A better way to go about doing this is just placing the live rock on the bottom of the tank, and then filling it up with sand. This way, your animals can't burrow UNDER the rock. That could possibly lead to rocks falling over.. and we wouldn't want that in a glass aquarium, nor an acrylic one.

 

[weeztankx]

Thankx for that link with all that good info melosu! But I am not sure what size sand would be the best? Do you reef guys have a size you like to use or do you have a few sizes that you use all at once? When i do my tank I a, going to do the 2.5 -3.5 thing I guess. With the live rock at the bottom with the sand all around but what kind of sand. Another question my friend told my that the LFS will give me some of there sand that is in there tank to help mine out is this a good idea or no? Sorry did't me to jack your thread bro!

 

[Zer0]

I prefer a finer sand, since it looks nicer and the inhabitants that live on or in the sand, find it easier to live on. Like some gobies and blennies like to lye on the sand.. so if it's rough or larger sized, it could damage their bottom fins. The sand i used was Aragamax bahama oolite. It's sugar sized grains, which means it's extremely fine. I know there are other sizes out there, but as long as you stay within the "sand" realm, and don't do into anything bigger, you should be fine.

 

[Kurt_Nelson]

I understand that aerobic bacteria break down the ammonia into nitrate, (nitrogen cycle) but what about anaerobic? (ammonia into nitrogen gas)

Ive heard mixed opinions about whether anaerobic bacteria is ok (therefore go with deep substrate)

OR

Stop the growth of anaerobic bacteria and only have aerobic bacteria (shallow substrate)

Im not sure if this anaerobic bacteria sounds like a good thing.. is this the "bad bacteria" that everyone talks about?

Ahhh... the "how deep of a sand bed" question. I think of ALL the things I researched when I started my tank, THIS was the most confusing one of all because of all the conflicting information/myths/conjecture out there. So I'm here to say... I think little bits of everything you've read is correct - but I don't know what bits those are. Here's my take of the whole thing...

From the majority of info out there, you don't really have a DSB unless you have more than 4" of sand. 6" is a better goal. The real gray are is between 3" and 4" - this is the no man's land where you don't have enough depth for anaerobic bacteria, but you have too much depth to keep a clean sand bed without disturbing the lower layers and causing issues.

With that said... my sand bed is between 3 and 4 inches! Go figure. I started out with 4", but just couldn't bring myself to add more. And as the critters moved sand around on me, and I've sucked some out over the years, I'd say my average depth is 3.5". Have I witnessed devastating effects? Nope. Over the 3 years my tank has been running, my nitrates have rarely gone above 2.0ppm, and everything is thriving. I can't say that it's due to my semi-deep sand bed, but it's sure not hurthing anything either.

Yes... DSBs can generate the infamous and dreaded "H2S" or hydrogen sulfide gas. Many things I've read makes it sound like the H2S builds up this huge bubble in your sand bed that will someday rise to the surface and kill your entire tank, fill your house with the smell of rotten eggs, and cause your entire neighborhood to be evacuated. I'm not doubting that a DSB (or any sand bed for that matter) can develop H2S, but my opinion is that what little gas builds up filters through your sand bed and bleeds off in small amounts that most likely are never noticed by the livestock. Again... just my opinion.

And just so we get things straight - aerobic bacteria is the stuff that lives on your rocks, sand, filters, etc. that turn the ammonia into nitrites, and the nitrites into nitrates. Anaerobic bacteria is the stuff that then turns the nitrates into nitrogen gas, which then escapes your tank in bubbles. All properly cycled SW tanks will have aerobic bacteria. Some SW tanks, depending on the filtration will have anaerobic bacteria. Both bacteria are "good". I'm not aware of any "bad" bacteria when it comes to biological filtration.

Yeah... the whole DSB issue is tough to digest. In hindsight, I stressed too much about it. If what you decide to go with doesn't work for you, then change it. Nothing we do is set in stone... or sand.

[Edit: Oh... and welcome to Aquarium Advice!]

 

[Zer0]

Another great post. You should throw this in the article section. I'm sure people will be asking this same question at AA for many more years to come. Still, thanks for sharing the knowledge and experience Kurt.

 

[lmetcalf]

Kurt, I feel much better after reading your post! I wondered how important the whole thing really was. I'm not going to stress over it anymore: I'm going to go with 2 or 3 inches because I think that looks good and it will be enough to house some critters

Thanks everyone for your replies!

 

[Zer0]

If anything, i would say go with 3"s. It would be safer and more comfortable for the critters than 2 inches, and may still be behind the boundary of all that anaerobic and aerobic bacteria stuff.

 

[weeztankx]

Ok guys I am going with 2 1/2 though 3 in the front and then up to four in the back. in the front I mean 2 1/2 to 3 in waves in the front and then slop it up in the back so I will have all diffent depths all over! Thankx guy! O how does my sand bed sound?