Deep Sand Bed with Undergravel Filter?

[SirRoadwolf]

Here is a topic I really haven't seen discussed anywhere. Back in about 2004 or so, I had a freshwater aquarium which I have a mix of natural sand and gravel in as a bed, with an undergravel filter. The aquarium was amazingly self sustaining...

Getting back into the hobby now, I read that some people are very much for DSB's while other are very much against them. Given my past experience, I am pro DSB... But I never see any discussion on the use of an under gravel filter, to help the water flow through the deeper part of the sand. I understand that the deeper bacteria will do better without much oxygen. So would a undergravel filter with a very slow flow rate be beneficial ? or will it to more harm than good?

I'll mention that in addition, my primary filtration would be a Sump external to the tank itself.

 

[TheEngineer]

There are some that use under gravel filters still. I believe @Paul B does.

 

[nautical_nathaniel]

I'm not sure if it would harmful or helpful, I just know that the purpose of a DSB is the provide a place where anaerobic (oxygen free) nitrogen-fixing bacteria can proliferate so an undergravel filter would take away this anaerobic zone or seriously reduce it.

I do believe it would also be a pain to take care of in terms of maintenance and that's generally why the hobby has gone away from them. I know a lot of folks still use undergravel filters though so maybe some folks in the #reefsquad can chime in with their thoughts or tag folks that still use them in conjunction with a DSB.

 

[TheEngineer]

Also, to some extent a plenum is kinda like an under gravel filter but it isn’t powered.

 

[jda]

Lots of people with remnant UGFs take the tubes out and have a plenum. UGFs are a great filter, but with so much oxygen, there is no chance to denitrify... so the DSB is not really doing what other DSBs do.

FWIW - you can get really good denitrification in just 3" of sand. This is my go-to depth.

 

[Dom]

I had one experience with under-gravel filtering. It wasn't a good experience.

When I broke down the tank, under the filter, there was a thick, black tar-like liquid. I wouldn't use one again unless I had a way of getting under the filter and cleaning it out as part of my maintenance. How would you do that?

 

[Lasse]

Watch my build tread. I use a DSB with a slow reversed flow of water through it.

Sincerely Lasse

 

[Greybeard]

I kept DSB systems, back in the day. A few observations:

Most stable, easiest to maintain system I've ever owned was a 240g reef with 300 lbs of Southdown sand in the bottom of it, populated heavily with as diverse a population of micro fauna as I could buy, mostly from Inland Aquatics and GARF. I could grow _ANYTHING_ in that aquarium... for about 5 years. After that 5 years, nitrates went through the roof, and I was unable to get them back where they should be. All my hard corals browned out, and started dying. Due to non reef related issues, I had to shut that tank down, shortly after I started loosing corals.

Most of my reefing club, from that time, were doing the same thing (we used to bring in Southdown Sand by the ton!). All experienced the same sort of results. Great way to keep a tank, for 4 to 7 years. After that, the nutrient 'sponge' that the DSB represents is exhausted, and things start to go south.

I never ran a plenum system, and the last time I ran an under gravel plate, it was under a 1" bed of rough (1/4" and larger) crushed coral substrate... probably about 1988. That system was fine... for fishes. Wouldn't have ever dreamed of trying to keep corals in it.

These days, it's probably all moot. There are known methods and techniques that allow a reefkeeper to maintain nutrient levels as low as you might want to go... too low, in some cases. Carbon dosing, zeovit, etc. Techniques that were simply unavailable back in the DSB days, and far superior to what we were doing then.

I loved my DSB system, and I'll always have fond memories of it, but that era is over, and IMHO, we're way better off with newer techniques.

 

[jda]

I know that this is kinda turning into a DSB thread, but I am not of the opinion that you can just leave them alone forever or they do stop working after a while. I do vacuum mine all the way down to the bottom starting in about year four. I do about 25% of what I can see every quarter so that I get the whole process done in about one year. This does remove all kinds of somewhat-harmless gunk and sludge that can "gum up the works" and appears to reset the clock on the sand.

I do like what the sand does for phsophate buffering as well as denitrification, so this maintenance is well worth it to me. I only do a little at a time so that the oxic and anoxic zones have time to repopulate. Once I get done with a section, the cucumbers and conchs hang out there a lot more.

 

[Cole12]

Here is a topic I really haven't seen discussed anywhere. Back in about 2004 or so, I had a freshwater aquarium which I have a mix of natural sand and gravel in as a bed, with an undergravel filter. The aquarium was amazingly self sustaining...

Getting back into the hobby now, I read that some people are very much for DSB's while other are very much against them. Given my past experience, I am pro DSB... But I never see any discussion on the use of an under gravel filter, to help the water flow through the deeper part of the sand. I understand that the deeper bacteria will do better without much oxygen. So would a undergravel filter with a very slow flow rate be beneficial ? or will it to more harm than good?

I'll mention that in addition, my primary filtration would be a Sump external to the tank itself.[/Q

 

[Cole12]

Using an under gravel filter on a DSB would completely defeat the purpose of having a DSB and creating an anerobic zone for denitrification.

 

[Lasse]

Using an under gravel filter on a DSB would completely defeat the purpose of having a DSB and creating an anerobic zone for denitrification.

Not at all - if you use a slow reversed flow it will instead make it a better denitrification tool. You can also ad some organic carbon to make it much better. If you place this in your refugium as a remote DSB - you will get som nutrients out for the macro too. I was forced to take out my reversed flow DSB after a year and take out my siporax that I used in the bottom. The bed has been running with a rather high reversed flow but the sandbed was total clean. At the moment - I run my flow with help of the redoxpotential in the bottom water. For the moment - between -50 and - 100 mV. Goal -> -150 mV. If it will be a little to effective - I rise the flow through it - make lesser denitrification

The graph show the redox last 24 hours - every top is an injection of water from the reversed system

​

Sincerely Lasse

 

[Lasse]

I had one experience with under-gravel filtering. It wasn't a good experience.

When I broke down the tank, under the filter, there was a thick, black tar-like liquid. I wouldn't use one again unless I had a way of getting under the filter and cleaning it out as part of my maintenance. How would you do that?

This is exactly what I want below my gravel - there is there the magic happens

Sincerely Lasse

 

[Swoody]

In my new tank I set up 2 2' x 2' sections of under gravel filter and have a powerhead on each section. I do not have a particularly deep sand bed and the areas where my UGF's are are mostly under my rock work.....will it help?? I sure hope so, but I don't see it hurting either. The gravel is nice and clean....been about 2 1/2 months.

 

[Dom]

This is exactly what I want below my gravel - there is there the magic happens

Sincerely Lasse

So that black, tar-like stuff is good?

 

[jda]

The black is an indicator that you have an anoxic process going - turning NO3 into nitrogen gas. I do not know what the black stuff is, but that is the goal.

 

[Lasse]

So that black, tar-like stuff is good?

The black is an indicator that you have an anoxic process going - turning NO3 into nitrogen gas. I do not know what the black stuff is, but that is the goal.

The black stuff is bacteria and other organic matter - and yes - it show that you have an anaerobe breakdown process taking place.

Sincerely Lasse

 

[siggy]

The black stuff is bacteria and other organic matter - and yes - it show that you have an anaerobe breakdown process taking place.

Sincerely Lasse

I often wondered why UGF was not popular. what would be the difference than a Bare Bottom or a UGF and aragonite base, I understand sand could easily mess things up but the flow threw the araginite would provide a huge surface area for bacteria. not to mention the buffering

 

[Paul B]

Oh No! Are you saying that UG filters are BAD!!!. OMG,, I just put one in my tank after I moved it. Should I tear it out
?

 

[Sallstrom]

You can even buy a ready sump system with a controllable DSB. Been available for some time in Europe. Was started as an experiment at Rotterdam Zoo in their large frag tanks. I like the idea, but haven't had the chance to build my own version yet(or I did but put in Siporax which was a mistake (leaking a lot of Si if it's in anaerobic area)).

Check out DyMiCo
http://www.dymico.com/