sand filter? newb Q's...

Sand beds don't really need filter plates (UGF or Under Gravel Filter), but if you add them, add a layer of quilt batting over them before adding the sand. This will keep the sand from flowing through the holes/slits in the plates.

Sand beds are a haven for anaerobic bacteria. Some people will say this is good and others will say it is bad. If you tend to be on top of your tank maintenance and water changes, then this can be a good thing because the anaerobic bacteria will consume nitrates (not desireable since you have plants (plant food)). By running UGF plates under the sand, you will prevent nitrate consumption so that your plants will have more food.

I think the advice you were given is because when an anaerobic sand bed is in the hands of someone who does not keep up on the tank maintenance, the bacteria can cause a bloom when large amounts of organics are introduced to the tank. This bacteria bloom consumes oxygen and can easily suffocate all of the fish in the tank. FWIW, this is the mechanics of the myth that over feeding fish will kill them.