sand bed crash??

[jd474]

i was recently talking about this with a colleague and thought i would post this question here, even though it's probably not the best place. We were discussing sand beds in very large aquaria (10 000+ gal.), where it is impractical to hydroclean the substrate, and what happens with that bacteria when it accumulates over a period of a decade or so. is it a 'ticking time bomb'? does nothing happen? will it crash someday? anybody have any thoughts on this? there are very few reef tanks this size in the world, and i know it is a question that has been somewhat tossed around amongst professional aquarists, but no one really seems to know.

 

[KarlBob]

How deep is the sand bed? I don't know anything about tanks that size, but I do know that a shallow sand bed in a household-sized tank acts differently than a deep sand bed.

Is there any way you could push a probe down into the sand bed, or bring out a small sample in a sealed container? In a hobby tank, taking a sample might disturb the entire bed enough to set off such a "time bomb", but in a 10,000 gallon tank, you might be able to grab a "core sample" from the surface of the sand to the bottom of the tank without disturbing the entire bed.

 

[jd474]

it varies depending on the spot, but there are 15 tons of sand total, roughly 6" to 10" deep throughout. we have tried hydrocleaning with large vacuums (6" x 36" cylinders), but it's just so big and so much sand, it really is impractical (plus it's sugar fine sand to boot).

 

[nebraskareef]

JD, what tank are you talking about in particular? Sulawelsi?

I have no suggestions, but wondering...

 

[billsreef]

Lot's of sand sifters, including sand sifting gobies Also good strong wave action to keep things flushed. Carlson surge devices work really well on large tanks.

 

[jd474]

<a href=showthread.php?s=&postid=15281902#post15281902 target=_blank>Originally posted</a> by nebraskareef
JD, what tank are you talking about in particular? Sulawelsi?

I have no suggestions, but wondering...

yes, the beach tank. and i don't know that anyone really has any suggestions or ideas what will/can happen. probably only time will tell i suppose. unfortunately only joe yauillo's tank at atlantis is the other reef tank similar to this size and age that i know of? i don't know what the folks at the georgia and stinehart AQs are doing with their monster reef tanks either.

 

[nebraskareef]

I know the sandbed is primarily silica, I wonder if grain size would play a factor in the number/type of bacteria that is actually colonizing the bed?

Are you guys considering swapping the bed, or is this just a "what if..." type of situation?

 

[jd474]

<a href=showthread.php?s=&postid=15282079#post15282079 target=_blank>Originally posted</a> by billsreef
Lot's of sand sifters, including sand sifting gobies Also good strong wave action to keep things flushed. Carlson surge devices work really well on large tanks.

it has a 400 gal CSD, keep in mind it is ~26 000 gal. and fish compatibility is an issue with a mature pair of dragon wrasses

Are you guys considering swapping the bed, or is this just a "what if..." type of situation?

just kicking the 'what if' around the other day after a pointless hour of hydrocleaning (and subsequently deciding not to do it again)

 

[nebraskareef]

When you say "hydrocleaning" - are you essentially just vacuuming the sandbed with a large tube, disrupting "dust" and leaving the sand?

If so, how deep are you guys going, and what section are you starting in?

This whole question has really got me thinking about this tank. I have a video from a few weeks ago, I'll upload it tonight so folks have a frame of reference, not that it will help

 

[jd474]

<a href=showthread.php?s=&postid=15282513#post15282513 target=_blank>Originally posted</a> by nebraskareef
When you say "hydrocleaning" - are you essentially just vacuuming the sandbed with a large tube, disrupting "dust" and leaving the sand?

If so, how deep are you guys going, and what section are you starting in?

This whole question has really got me thinking about this tank. I have a video from a few weeks ago, I'll upload it tonight so folks have a frame of reference, not that it will help

just gravel vacuuming. i used a 36" long, 6" clear pvc vacuum connected to an 1.5" line (it sucks a LOT of water). i could easily go 6" deep and pull solid brown detritus non-stop. i probably covered about 30 square feet, or about 1/8th of the total area, starting at the back and working toward the coral stands.

 

[chercm]

<a href=showthread.php?s=&postid=15283669#post15283669 target=_blank>Originally posted</a> by jd474
just gravel vacuuming. i used a 36" long, 6" clear pvc vacuum connected to an 1.5" line (it sucks a LOT of water). i could easily go 6" deep and pull solid brown detritus non-stop. i probably covered about 30 square feet, or about 1/8th of the total area, starting at the back and working toward the coral stands.

do u have any picture for this ?

 

[jd474]

<a href=showthread.php?s=&postid=15284050#post15284050 target=_blank>Originally posted</a> by chercm
do u have any picture for this ?

of the vacuum, or me doing it?? we have over 5000 people come through daily, so getting a pic of me doing it is a little difficult. if you want a shot of the vacuum, i'll get one on thursday when i get back to work

 

[MrPike]

What made you decide to vacuum it? Im assuming you noticed some sort of pest, and are trying to control it, which to me says the sand bed may already be "crashing"

I don't think its capable of just one day exploding, although having some stray circulation pump aimed at the sand bed releasing hydrogen sulfide may qualify.

 

[jd474]

<a href=showthread.php?s=&postid=15286358#post15286358 target=_blank>Originally posted</a> by MrPike
What made you decide to vacuum it? Im assuming you noticed some sort of pest, and are trying to control it, which to me says the sand bed may already be "crashing"

I don't think its capable of just one day exploding, although having some stray circulation pump aimed at the sand bed releasing hydrogen sulfide may qualify.

we were hydrocleaning because it hasn't been done in 8 years, and there is a huge detritus build up. there are no 'pests,' the concern has more to do with the bacteria 'crashing' and water quality becoming too poor for the corals. i'm not sure what you mean by 'stray circulation pump aimed at the sand bed'

 

[MrPike]

Im not sure how your flow is designed, but sometimes a powerhead will fall from its mount and be aimed at the sandbed. It can really mess up the tank, the sandbed can then crash the tank.

 

[chads 385]

Low PH

Low PH

Hey guys im having similar problems with my tank. Only a 400 gal its been running for 3 years and my PH has really droped 7.6 everything tests fine corals are doing fine but I lost some fish. I do weekly water changes all my buffers are good but I can't get my PH to come back up. The only thing I can think is my sand bed has crashed. Im afraid to pull all the sand out and make things worse. What do you guys think?

 

[MrPike]

Low PH could be - Excess C02 in your house, Low Alkalinity, or as you suggested, a full sand bed. I would double check the first two before blaming the sand bed though

 

[chads 385]

low ph

low ph

Alk is fine 10.2 as far as the co level in my house thats hard to say I have never had a problem with ph before just in the last month and there have been no changes or additions to my tank. I guess i could open some windows to see if that helps but its been hot out and I have been running the air conditioner.

 

[surfjeepzx]

To answer your question as to whether a sandbed can crash a tank, I beleive the answer is yes as I just experienced it. My sand bed was full so to speak. The detritus had overcome the sandbeds ability to act as a biological filter. Phosphates skyrocketed and within a weeks time I almost lost my entire SPS system. Once I discovered it was phosphates I started backtracking and eventually it came to the sandbed. I had to vacuum (remove) the entire sandbed and clean it.

I live by the ocean so I simply took all the buckets of sand to the beach and loooked like an old maid doing laundry on a scrub board as I sifteed the sand clean of detitus. Then I replaced the sand and now the tank is making a slow recovery.

For a tank your size I have an idea.

If your are familiar with a well point used with ground water wells, it is a pvc pipe with razor fine slits for some length of the pipe that is designed to pass water and reject sand. If you were to take a section of this pipe and make a type of siphon that would draw water slowly through the sandbed and into the pipe you could make an automated type of sandbed cleaner.

Using a vacuum pump connected to section of hose and then the well point pipe (with the end capped), you would submerge the pipe into the sand much like sinking a well. Start the vacuum and aloow the water to be drawn through the sandbed which would carry with it detritus and leave the sand in place. This would be a trial process as you would have to determine how long to leave the well point in the sand before it had exhausted that area of detritus. By simply observing the water clarity or using some type of filter media to determine acceptable water clarity you could determine when to move the well point to another section of sand.

The idea here is that you aren't ever actively in the tank cleaning. You simply insert the wellpoint into the sand and monitor the water being extracted until it meets your standards.

You would also have to determine the extraction rate (vacuum rate) of the water as to determine the best rate at which detritus is being removed.

Well points typically only come as a 2" - 3" pipe so that's why this would be impractical on a small tank but in my vision could be used on a tank of the size you are maintaining.


OK fire away. I have other ideas for filtering the water such as running it through a standard type pool filter housing containg a pleated filter before returning it to the tank.

By the way Lowes sells Well points in the plumbing dept .

 

[wld1783]

My tank is much smaller but KISS, Keep it Simple.

Each tank is a Captive Reef Ecosystem and every thing has to be planned....

Who eats the fish waste...Soft coral, SPS, LPS, Micro Fauna?

How much hydrophobic DOCs will the skimmer handle? What about the hydrophilic DOCs?

Silica for sand?...Harsh on the micro fauna...Sharp edges

Types of fish that will prey on the micro fauna. Do they have enough refuge?

IMHO in an established ecosystem, a sand bed should not crash...My 12" DSB (southdown) in a small 440gal tub has been doing fine reducing nitrates for over five years.

As far as phosphates what type of export are you using?

My only problem is coralline algae.


Bill