How much substrate?

[paulg]

I have about 1.5 inches of live sand and 80lbs of live rock ion my 75gal tank. Is that enough sand?

[ChilisREasy]

yep you can have as much as you want, even none at all, your live rock holds most of the good bacteria anyway.

[hng]

It depends on what kind of setup you want. If you are looking at the sand strictly from a biological standpoint (converting ammonia to nitrate) then that's more than enough. In fact, you don't really need any sand at all for that. Some people prefer a deep sand bed (DSB - 4 inches or deeper of fine grade sand) because denitrification occurs in the bottom layers and nitrate is converted into nitrogen gas. There is a drawback to the DSB though. Many people feel that the sand bed becomes a sink for all of the waste material in the tank and there will come a time when the sandbed can no longer absorb any more and it will begin to dump all of that waste back into the tank. This is also known as the old tank syndrome, where a mature established system suddenly and unexpectadly starts to go down hill. Also, depending on how deep your tank is overall, a DSB can significantly decrease the amount of space you have for rock and fish. HTH

[paulg]

Ty

[bwillcutt]

This topic is always interesting here in my area between us reefers, some love deep sand beds and others like hardly any sand. I am in between and not had any problems each to his own on this one!

[Tommy Gun]

Even though I realize that I am new to this forum, I have been around for a little while and the most common advice I have ever heard, was to keep a DSB of 3 to 4 inches. The advantage to sand is that it provides much more surface area for benificial bacteria to live/thrive upon and as was already pointed out, can have benifits like denitrification.

Many people feel that the sand bed becomes a sink for all of the waste material in the tank and there will come a time when the sandbed can no longer absorb any more and it will begin to dump all of that waste back into the tank.

I agree, but have also heard and learned with my own tanks that this can be avoided by stocking some good sand sifting livestock such as certain snails, seastars, and even some fish. One somewhat unique 'tip' I have tried more recently was the addition of a substrate heating cable to help maintain a more steady and constant water flow through the substrate. The jury is still out on that one, but if the theory works, it would be the same as using the highly effective biological filter, an under-gravel filter, without all of the possible problems associated with doing so.

[hng]

this can be avoided by stocking some good sand sifting livestock such as certain snails, seastars, and even some fish. One somewhat unique 'tip' I have tried more recently was the addition of a substrate heating cable to help maintain a more steady and constant water flow through the substrate. The jury is still out on that one, but if the theory works, it would be the same as using the highly effective biological filter, an under-gravel filter, without all of the possible problems associated with doing so.

There is no hard fast rule or absolute when it comes to sand beds, but I will provide the common counterpoints. While it is true that sand sifiting critters will help keep detritus off the top layer of the substrate, they will only delay the inevitable overload of the substrate. How much of a delay depends on how effective they are. Detritus will get down into the deeper layers of the substrate. It is doubtful that sand sifting critters will go all the way down to the bottom of the sandbed and if they do, then the oxygen gradient will be ruined and denitrification will not occur. Same thing is true for the heating cable. You do not want efficient oxygenation of the entire depth of the sandbed if you want denitrification because you need some bacteria that live in hypoxic conditions to convert nitrate to nitrogen. If you do produce a well oxygenated sandbed, then you will have a nitrate factory (much like a wet/dry filter) which will create the need for more frequent water changes. That's the irony of the reef tank, you want the nitrogen cycle to work but not so well that the protien skimmer doesn't get a chance to remove wastes before it is broken down. That's one of the reasons why bare bottom tanks work so well.

[ChilisREasy]

well you can always use those aqua-cleaners & sweep the sand bed in little patches every month till cyano is gone works for me & no bad side effect either !

[Loverotties]

I've got 3".

[Geoff]

i have no sand at all.

having a DSB is a good thing if you are just getting into the hobby. it will allow you a couple of years of getting your knowledge down before you will need to replace the entire sand bed again. at that point you may figure out that a sand bed is not what you want.

think of the sand bed as the tanks septic system. at some point you will need to pump it out and start over. no sand means you need to get the poo out as often as possible. for me i do water changes every week, and this is working fine for keeping my system clean. you should be doing water changes every week anyway to keep the levels up and to siphon out detritus that builds up anyway.

G~

[Tommy Gun]

Well, I might not be getting off on the right foot here, but I have to disagree...

While it is true that sand sifiting critters will help keep detritus off the top layer of the substrate, they will only delay the inevitable overload of the substrate

...with this. My reason is because, of any substrate, sand has to be the least likely to trap detrius so, unless we are talking long long periods of time (e.g. years), it is not like 'old tank syndrome' is something that is just going to 'pop up' one day when we least expect it.

As far as sand sifting livestock goes...I think that there are a lot of other 'items' which some of us may not consider adding, or trying to protect which can help out a lot. For example, I recently learned the great benifits of a strong bristleworm population as being great for keeping at least the first inch or so of sand nice and oxegenated.

Personally, the denitrification isn't enough of a 'bonus' for me to feel that a DSB is a good idea...meaning there are other benifits which make them something to look at. For example, when compared to larger substrates like crushed coral, sand is a better alternative because uneaten foodstuffs, wastes, etc... are much less likely to become trapped in the tank for long periods of time (i.e. they can be vaccumed off the top of the sand easily).

True, no substrate is an option...but for some of us, substrate is more pleasing to the eye. In fact, I also sort of 'need' the substrate to hide my system of faux-powerheads I made using some PVC pipe and a couple 1200 gph pumps.

In the end, my true point is that IF there is going to be a substrate, sand might be a good option, and if so, it is probably better in 2 or more inches (if not three or more). In fact, any substrate can help to make up for a lack of live rock, but sand more so than others.

Once again, just trying to make a case for a DSB since the topic of this thread is 'how much substrate'...and of course, only making that case in a constructive manner.

[hng]

Originally Posted by Tommy Gun

so, unless we are talking long long periods of time (e.g. years), it is not like 'old tank syndrome' is something that is just going to 'pop up' one day when we least expect it.

Yes, we are talking about years for this to occur. Exactly how long is dependent on a person's cleaning crew, how much they feed, how much they clean, and how much sand they have. Even a tank that has it's substrate cleaned meticulously will eventually have waste buildup. And if you try to vacuum the deep layers of a DSB, then you have to beware of releasing some toxic junk from the hypoxic layers of the tank.

Originally Posted by Tommy Gun

In the end, my true point is that IF there is going to be a substrate, sand might be a good option, and if so, it is probably better in 2 or more inches (if not three or more). In fact, any substrate can help to make up for a lack of live rock, but sand more so than others.

Very true. I am just providing the counterpoint to the DSB method. There is no right or wrong, no perfect method. Everything has it's ups and downs.

[Geoff]

the big problem with a sand bed is that they absorb phosphates. actually any calcium carbonate substance will absorb phosphates. this is what they do very well. old tank syndrome is just another name for a phosphate tank crash. even sand bed critters poo. nothing will eat this poo. at some point poo is so broken down that nothing will eat it. this sits in the sand bed where the phosphates will be absorbed into the calcium carbonate. the only way to remove phosphates from calcium carbonate is through bacterial turgur. unfortunately bacterial turgur does not work on a sand bed. gravity gets in the way. it works very well on LR as long as the LR is suspended and good flow below them. this keeps the bacterial flock from sitting in the same spot and allowing the phsophates to leach back out and absorbed by the LR again. getting the bacterial flock in suspension allows the skimmer to remove it before it becomes absorbable.

having a sand bed also allows phosphates to be wicked up by LR. this is why cyano starts at the bottom of the tank then works it way up the LR to the top. that whole calcium carbonate phosphate absorption thing. if you have a sand bed it is a good idea to suspend the LR above the sand bed.

in a reef system phosphates are you enemy. it has only been in the past 5 years that this has been revealed. the easist way to keep phosphates to a minimum for me is to have a BB tank. i just do not have the desire to replace a sand bed every X number of years. i have done that once and once is enough. i am siphoning out all detritus once a week. it takes me 10mins to do a full detrital removal. the huge amount of flow(12000gph in a 125g) in my system allows 99% of all detritus to make it to the sump where siphoning is a breeze. every 3-4 months i will do a quick siphon around my clams in the display, but other than that i very seldom put my hands in the display.

Tommy Gun, you will not get on a wrong foot here. we want people to question and give a secondary view point. this is not a place for my way or the highway. there are a few monster threads on TRT that really get into the whole chemistry of DSB's and their shortcomings. DSB's have a place in the reefing community, but they should not be used as most commonly described in the community. each subtrate has its advantages and dissadvantage. it is up to the reefer to weigh these and decide which is better.

G~