This is a response to a PM asking how to keep crushed coral.
Crushed coral has its advantages over sand and its disadvantages. The main point is that you need to know the differences and set your tank up accordingly.
Live sand is better for some organisms. Sand sifting starfish, for example, will do much better in a deep sand bed than will crushed coral. However you also run the risk of it disturbing your sandbed too much, exposing crucial bacteria to oxygen and killing it. If enough bacteria gets exposed to oxygen you can have an unsafe nitrate spike.
I like crushed coral because you can still keep a majority of the organisms that people can keep with sand and you don't run the risk of a tank crash by overly disturbing your substrate. People complain of crushed coral being a nitrate factory. It is if you have it so deep that your hermit crabs and snails can't reach the junk that settles at the bottom of your tank.
Crushed coral is very coarse and because of this it does not house nitrate consuming bacteria very well. This, to me, is an advantage because the substrate in people's tanks can get disturbed very easily due to rocks shifting, tank inhabitants moving it and owners who need to move their tank. To me, letting your tank run off the bacteria in the sand bed is too much of a risk. Our tanks are not like the ocean. It's not like you can move a little sand around and crash the ocean... but you can your tank.
I prefer to let the filter system and live rock house the bacteria. It does not matter how much you move live rock, you will not kill the bacteria in it like you can with moving sand. If you want to use crushed coral you need to make sure you keep it shallow. Since it won't be housing nitrogen consuming bacteria you need to keep it shallow enough for your clean up crew to reach the dirt in your tank. Keep it too deep and you will have nitrate problems that everyone else complains about. I recommend a depth of no more than 1 inch. You want just enough to cover the bottom. By keeping it shallow you also reduce the risk of your rocks collapsing by sand sifting organisms burying underneath.
To me, crushed coral is easier to clean. You can vigorously vacuum the crushed coral and get it spotless while deep sand you can't because of the risk of killing your bacteria. Over time you can have lots of sludge build up at the bottom of a sandbed and if you don't have it set up right, it can build up dangerous hydrogen sulfide gas which is poisonous to your tank. If your sand gets disturbed, this hydrogen sulfide can be released and can harm your tank. This is a problem for people who keep their sandbed (and crushed coral) too deep. The beneficial bacteria grows in low oxygen zones... not oxygen free zones. If the substrate is too deep then you run the risk of hydrogen sulfide buildup due to oxygen not being present. That's why I prefer to just skip letting the substrate be my filter system and let the safer rocks and plants do it for me.
To keep crushed coral:
- No deeper than 1 inch
- Get lots of live rock to consume nitrate
- Recommend a refugium with live plants which also remove nitrate (and won't crash)
Get a good clean up crew (snails, crabs, urchins)
Use plenty of powerheads to keep the water moving. Will tolerate higher flows than sand without clouding up the water.
If it ever gets dirty, stir it up so that the dirt can get sucked into your filter system and emptied out with your skimmer. Run a prefilter in your system to catch waterborne dirt and rinse it out as needed.
Since I've had my tank I've had to move it 3 times. At no time did I have a nitrate spike. I simply packed up the tank and put the inhabitants into buckets and then set it back up in its new location the following day. Since I didn't rely on my substrate for filtering my water (I have live plants and rocks instead), I didn't run the risk of crashing my tank by moving my substrate around. My tank was set up and running as good as ever with no nitrate spike or cycle whatsoever. If I had a deep sand bed this would have been a different story in that I would have had to wait a month for the bacteria to recolonize enough to support the inhabitants in my tank, stressing them while they waited in quarantine.
Back to your original question, in a new tank particles will remain suspended until you starting building up organic waste in your water column. The particles get weighed down as your tank matures due to organic sludge sticking to them. Over time it will clear on its own. I would recommend letting your tank cycle for a few days and then turn your skimmer on. It will really clear up the water. If water clarity is very important to you, you can get the water so clear that you almost can't see it if you use ozone. I feed ozone into my skimmer with an airpump and I regulate it with an ORP controller. The water is so clear that sometimes the fish look like they are floating in nothing.
