fluidised sand bed

[ghostface]

anyone running / ever run a fluidised sand bed? i am thinking of setting one up - i have gone BB, but refugium is still set up with about 4 inches of sand. still want to have the aragonite there for stable PH, but dont want to deal possible future DSB issues.

current setup=200l display, 70l sump, deltec AP850. corals / fish / lotsa rock

any suggestions?

[lduncan]

still want to have the aragonite there for stable PH, but dont want to deal possible future DSB issues.

Aragonite is limited in it's buffering abilities to the point of being insignificant. People think it is significant mainly because bacteria dissolve it within their micro environments as a source of carbon, this doesn't get released to the tank as carbonate alkalinity, it's consumed by the bacteria which liberate it.

Personally I'd flag it altogether.

Layton

[ghostface]

ok layton what would you suggest? the obvious option would be to remove the fuge / sandbed altogether, but i have no calcium reactor, and would rather not get one.

doing 1/5th water change every 2 or 3 weeks.

i want to keep the tank as nutrient-free as possible, but also as simple as possible.

all other info i can find says that aragonite will keep PH stable. do you have links to any papers saying otherwise?

[ghostface]

just looking for a bit of direction on what to do with the tank. ideally i want to remove the sand altogether, but dont want to lose the positive effects of having it there - nitrate removal, PH stability etc.

[Ira]

The advantages are minimal unless you have a DSB(Other than aesthetics and sand sifting animals) so I'd just get rid of it completely. Replace with heaps of liverock or something.

[Sharkey]

Hi Ghostface i think what your doing is verygood. One of the principal benefits to deep sand bed methodologies is the potential for natural nitrate reduction (NNR). The speed and extent to which a DSB can reduce nitrate in an aquarium amazes many aquarists… especially those that have struggled with nitrate control for any length of time through other means. The benefits to an established tank with the upgrade to a DSB are apparent in just a few weeks with potential for complete nitrate reduction (to “zeroâ€)!Anthony Calfos words not mine. And every thing i have read says the same thing about the buffering layton is correct in saying that bacteria dissolve it within their micro environments but there is no deniying the facts that it has been proven with out a doubt to buffer water giving a more stable ph and better alkalinty aragonite is to be favored for it’s better solubility and buffering capacity in seawater (providing necessary bio-minerals, buffering pH, and supporting calcification). Aragonite can begin to dissolve, in fact, at a high pH over 8.0 (a still safe level for marine life), Ps i do the same thing but have it in my display tank !!!

[lduncan]

The advantages are minimal unless you have a DSB(Other than aesthetics and sand sifting animals) so I'd just get rid of it completely. Replace with heaps of liverock or something.

I'd agree with that Ira.

Ghostface:

If the sand is performing denitrification then it will be storing phosphate and metals etc.

pH stability isn't really determined or helped to any large extent by the sand. It's determined by alkalinity and atmospheric CO2 levels.

I don't have any references as such for this, but my reasoning for sand not being as significant buffer as some think is the following.

From a chemistry standpoint, the solubility of calcium carbonate in water at a pH of 8.3 is around 25 ppm, at a pH of 8 it is close to 75ppm.

In terms of alkalinity (which is what the calcium carbonate sand turns into) a dkH of 10 (3.5meq/L) corresponds to a calcium carbonate concentration of 178 ppm

So the calculated solubility of calcium carbonate at normal tank pH is 25ppm, this isn't taking into account the common ion effect (which can significantly reduce the solubility due to the presence of a common ion which may already exist in solution) this is well above the concentration which already exists in solution (178 ppm) which means that bugger all is going to dissolve chemically.

The reason why the sand eventually does dissolve, is because bacteria create acidic micro environments which react with the carbonate to liberate the carbon they need to live and reproduce. Of course bacteria aren't perfect, and they leak, just like algae, so small amounts may make it into the water column. But the majority of this will be used by the bacteria themselves, otherwise they wouldn't go to the effort of creating these micro environments.

Bacteria are a huge consumers of alkalinity. The bacterial activity in sand beds means that they can be significant consumer of alkalinity. If anything ditching sand can result in a drop in alkalinity demand, and therefore less chance you may need a calcium reactor.

Depending on what you are keeping, you may not need a calcium reactor. Kalk may be adequate.

To me the only positive effects I can think of from having sand is aesthetics, and nitrate removal.

So I'd get rid of it altogether if you want to go the BB route.

Layton

[lduncan]

but there is no deniying the facts that it has been proven with out a doubt to buffer water giving a more stable ph and better alkalinty aragonite is to be favored for it’s better solubility and buffering capacity in seawater (providing necessary bio-minerals, buffering pH, and supporting calcification). Aragonite can begin to dissolve, in fact, at a high pH over 8.0 (a still safe level for marine life), Ps i do the same thing but have it in my display tank !!!

Where has this been proven, any numbers for those claims?

[ghostface]

wouldnt rock also store phosphates and metals then, if it was performing denitrification? i have plenty of rock, both in tank and first chamber of sump. i wonder if this will be enough..... anyone else have an opinion on the aragonite - PH thing, or see any pitfalls with removing sand / plants in fuge, leaving tank completely sandless?

if sand was used in a fluidised form, then surely it wouldnt store phosphates etc nearly as much as if crud was allowed to settle on it, as with a sand bed, only react to the ph changes and [depending on whose side you take] release carbonate.....

[lduncan]

Well when you remove all the sand, you no longer have a sponge absorbing nutrients, so you can't afford to let detritus sit and rot in the tank, otherwise you will get phosphate and nitrate accumulation. It needs to be removed asap. If you don't have plenty of flow to keep it in suspension until it is skimmed out, be prepared to be siphoning relatively often.

You've got a good skimmer, so as long as your flow is good, then it should be low maintenance.

Layton

[lduncan]

wouldnt rock also store phosphates and metals then, if it was performing denitrification?

Yes to a limited extent. The extent is dependant on the cleanliness of the water (and sand if any), whereas the amount stored in sand is independent of water quality. All due to gravity and bacterial turgor.

So if your rock is in clean water and sand, it will be storing minimal crap.

i have plenty of rock, both in tank and first chamber of sump. i wonder if this will be enough.....

It should be enough. Tank bioload using this method is mainly determined by your skimmers ability to remove crap before it breaks down.

if sand was used in a fluidised form, then surely it wouldnt store phosphates etc nearly as much as if crud was allowed to settle on it, as with a sand bed, only react to the ph changes and [depending on whose side you take] release carbonate.....

No it wouldn't store crap, but then it wouldn't have any benefits either, it won't be performing denitrification or looking good.

[Sharkey]

Layton Im not saying to use this as a method to dose your tank. Only as a supplement. The main reason for the DSB for me is NNR. but I do want to read more on

Bacteria are a huge consumers of alkalinity ?

Where can I read more on that?

[ghostface]

cool. cheers for spending ur 2000th post on me rekon the jury's still out on the aragonite - PH one though will have to do some more research..

[lduncan]

Layton Im not saying to use this as a method to dose your tank. Only as a supplement. The main reason for the DSB for me is NNR. but I do want to read more on

Where can I read more on that?

Well all life on earth is carbon based. Just so happens that alkalinity is the largest source of carbon in our tanks.

It's kind of like asking for more info on why plants are huge consumers of CO2.

quick google search comes up with this:

http://www.sigmaaldrich.com/Brands/Fluk ... ology.html

amazing the stuff you can find if you look

If anyone wants I can run through the maths of the chemistry behind the carbonate sand not providing any significant buffering capacity. It'll take a few pages though.

Layton

[ghostface]

Layton go hard if you want to put that info up. im sure it will be of use to alot of people.

[lduncan]

Layton go hard if you want to put that info up. im sure it will be of use to alot of people.

Or confuse people I'll give it a go. I'll do it over a series of posts here:

http://www.fnzas.org.nz/fishroom/viewto ... 738#106738

[wasp]

Ha Ha, lots of differing information as usual

Ghostface you idea of a fluidised sand bed has merit, and also drawbacks. On the plus side it will not become a phosphate or heavy metal sink, and it will also provide excellent ammonia and nitrite reduction. On the negative side it will provide no nitrate reduction, because this is accomplished in a low oxygen environment (why the bottom part of DSB's are good at it ), a fluidised bed will obviously not be low enough in oxygen.

As to buffering, there will be a slight effect. Depends on a lot of other factors in your tank, but as a general rule other buffering should be used also, the ph has to drop too low before the carbonate sand will supply buffering of any significance. Extremely unlikely carbonate sand will maintain PH at 8.0 or better in a tank. Not saying impossible, but it would be rare to find an example.

Easiest way to maintain PH, calcium, and alkalinity, without klutzing up with lots of equipment, would be kalkawasser. Cheap too, if you don't buy the genuine article.

[ghostface]

cheers wasp, thats what i was after......

do you think that a decent amount of rock will be able to perform enough nitrate reduction? i guess its hard to say, without examining the bioload etc of the tank.

one way to find out i guess...... out comes the DSB

[wasp]

Yes, rock is all you need. The recommended amount is 1 kg rock to 8 litres of water, but the trend is to less rock than that now, we have better skimmers etc.

If pulling a DSB, there is sometimes an ammonia / nitrite spike as the rock suddenly has to deal with more waste & takes time to adapt. Best plan monitor ammonia & nitrate & reduce feeding to minimum for a few days if there is a problem.