Substrates in marine tanks the good the bad the ugly.

[Max]

Hello!

Been a little while since I've been on a rant so.... no better time than the present.

Crushed Coral is one of the most evil things you can put in your tanks. It won't compact enough for denitrification and it doesn't have nearly as much surface space available as live sand. IMHO it's the very worst thing that you can put in your tank . It traps all of the detritus in your tank everything from feces to dead critters and they just lay their and rot as most of it is not accessible to the small life in your tank.

At first there are no problems then it turns into a great big old nitrate factory. Think of a kitchen sponge that never gets changed that you use for cleaning your kitchen, bathroom, walls etc. and you'll get the idea. If you have a reef or mixed invert fish tank it really is the kiss of :thud:.

A lot of first time s.w. keepers are directed to this by their lfs if they do advise it please don't listen. The only things it's good for is a calc reactor or if you have a lot of burrowing critters you can mix a couple of hand fulls in your sand to help with support.

If you have a crushed coral bottom there are 2 ways to remove it . First just take it all out and replace it with a sand bed or deep sand bed. If you do that keep an eye on your water conditions for a while after that and make sure you don't have a mini cycle. The 2nd alt for the cautious or people with larger tanks ,"50 gal and over I'm a chicken", is to remove 1/2 at a time. It takes a lot of work but, there is still quite a bacterial population in the c.c. "not a 10th as much as in sand", so you'll greatly reduce shock if you do that.

Next deep sand beds and normal sand beds what everyone needs to know.

Deep sand beds are the best IMHO for the long term health of your tank. They provide a home for denitrifying bacteria and a place for your infaunal critters to live. It also removes any need to really clean the bottom of your tank! Anything that you can add to your tank that removes waste and increases diversity is a good idea. The amount of surface space available is a great home for bacteria. It also looks much,much better IMHO and is more natural.

Deep sand beds do have issues in highly stocked tanks over a period of years they can start to release phosphates into your water column. IME if you don't overstock or over feed your tank this should take several years to occur. Also if you have sufficient populations of algae in a fuge or in your tank it should help to mitigate these issues.

You can also just go with regular 2 or 3 inch deep sand bed vs. the 5-7 inch deep dsb . It doesn't provide as much denitrification as a dsb as there isn't a very large or any anoxic area. It won't leach out phosphates though or not IME. As an alternant you might consider a normal sand bed in your main tank and a deep sand bed in your fuge to get the best of both worlds. It's a lot easier to change out things in a fuge vs your main tank.

A lot of people in S.W. started out in F.W. where gravels of various sizes is the norm. That's not the case in the oceans constant tidal action quickly wears down rubble to sand. Most critters in s.w. haven't evolved to inhabit such an environment. A few pebbles and maybe a hand full of c.c. if you have burrowing critters won't hurt anything as it adds some structure.

bb or bare bottom.
This isn't one of my favorites I don't like the look. That being said though it's really easy to keep it clean if you have a reef and it also doesn't have any issues like leaching phosphates etc. You do have to stay on top of your tank maintainance.There isn't anything,"well as much" in the tank to deal with waste,"like in a dsb or sb" It is a perfectly workable situation in a marine tank.
hth
max

[Lobo.]

what do you do to prevent phosphates from leaking from a sandbed?

what about UGF filters, how do they affect sandbeds as oxygen is sucked futher into it, and there is a big gap in the bottom of the sandbed?

[bencozzy]

if your substrates leaking po4 the only way to fight that is to replace the substrate or get a phosphate removing media(rowaphos and polyfilter)

and as for a ugf i believe it would work the same as in FW, probably would kill all the sand bed critters???

now you can use a ugf to make a plenum, run the ugf for about a month then just pull the risers out and it will go anoxic.

deep sand bed are good for FOWLR or reef tanks but for fish only's a thin 1-2" bed will work just fine, easier to vaccum IME.

[Max]

Most people don't use ugf's or plenums anymore. They are more trouble than they are worth in general. I'll post a little about deep sand beds and phosphates over the next little while.