Can I use marine sand with an underground filter?

Question

I'm still trying to figure out the best filtration system for my 29 gallon hex saltwater. Would it be better to use crushed coral and the underground filter? Or remove the underground filter and use sand and other filters??

I also have an aquaclear 50 if that helps :)

Answer 1

I would advise against the crushed coral. The pieces are relatively large (about the size of aquarium gravel at times) and pieces of food can get trapped between them. This may be a problem if you don't have the undergravel filter with the reverse flow - as the food falls down where the fish/inverts aren't able to get to it as easily, it decomposes and adds wastes (ammonia > nitrate) to the tank.

As far as sand, it depends on how you're using the term. If this is sand as in what you find on a beach, the particle size is too small to use with an undergravel, and if it's actual sand (silica) it doesn't have any of the pH buffering capabilities that aragonite sand does - this not only helps keep the pH from falling below 7.8 (it should be in the 8.2-8.4 range), it adds calcium and magnesium which your fish and inverts will use. This link gives a good idea of the types of substrates available for saltwater, and has a chart comparing them for various characteristics: http://www.caribsea.com/pages/products/dry_aragonite.html

An option you may not have considered for filtration is to continue to use the Aquaclear you have, but to buy additional extensions for the intake tube. This way, you could make the intake extend to the bottom of the tank, and as water is moved through the filter, the oxygenated water near the surface will be drawn down to replace it. As long as you keep the water level in the tank to behind the trim at the top, this shouldn't produce any additional strain on the motor, unless the guards on the tubes catch too much debris - you'd just need to remove and backflush these periodically.

Answer 2

its whatever you like.

personally.... i have live sand for the bottom which needs to be avoided with a UGF. i find that the sand does alittle better for bio-filteration like live rock.

You can use a HOB aquaclear, sand, and maybe an internal filter.

On my saltwater 20, i have a powerhead with mech filteration, internal fuval 40 somthing. and a aquaclear 70.

It isnt that bad and it has plenty of current for the reef sett-up.