The idea behind having a substrate in an aquarium is it simulates a more natural environment, gives the beneficial bacteria more surface area to grow on, encourages natural behavior of some fish, something to anchor live plants in, etc. But you certainly don't need a substrate in an aquarium to keep it healthy, as long as you have a very well cycled filtration system.

Cloudy water is usually caused by a bacterial bloom. Blooms happen as a normal process during the cycling of a tank or as a chronic symptom of an unhealthy, unbalanced tank. This can happen with, or without substrate.

Hi
A fascinating subject as in theory it would be possible
to turn all waste products back into gaseous nitrogen. After all this is what happens in the"real' world .lol
In practice it's very difficult to arrive at a "perfect "balance..in a fishtank lol
Depending on how deep you want to get into this just a basic knowledge is all that's required The cycle WILL happen no matter how you set it up lol.
For the average fishkeeper the usual methods are certainly adequet BUT there are a mutitude of other methods . to get the same result andd far more enjoyable to look at !!!
To the above I might add the MOST impotrtant detail.Water changes no matter what system of filtration you choose. There is an old fishkeepers saying "The solution to pollution is dilution." To my mind the only solution . gary

I've primarily been a saltwater hobbist for many years. The trend now especially in reef tanks is to have bear bottoms as it is easier to remove organic waste. Given time these substances break down into various toxic elements such as nitrates and nitrites. The former is a serious problem exasperated when there is a medium of gravel or sand. I always have had sand in my tanks because of some tank inhabitants but struggle with maintaining low nitrates.

Johnsp,

I've also had saltwater for many years now, particularly reef tanks. Bare bottom is sorta going out in favor of a shallow bed.

Albert,

Substrate gravel, sand, whatever, is used as a biological filter. This works very well until it becomes "clogged up". Depending on the depth of the substrate, granular size, material composition.... depends on the life cycle of your tank.

I am one that is in favor of a substrate. Having said this, I use fairly small particulate in my saltwater tank. It is a reef system and totally different from a freshwater setup. However... Freshwater, from what I remember years ago, works well as a bio filter as long as the water parameters are checked frequently and appropiete measures are taken. Meaning... Making a vac of the substrate, after that, stir it up just a little and keep doing a vac. I would stuff the vac into the substrate and get the gunk out.

Keep an eye on the PO4 reading. Just keep the water changes going on around 10 to 15% water volume a week. You should be good unless way overstocked.