help / advice needed regarding cloudy tank

My 55 (ha) in my living room has sand in the bottom. I have a sponge filter in it but inside of the tank looks like dust floating around. This dust must be coming from the plants and my sponge filter is just not taking care of it.
I do not care for the HOB filter so what I thought I would do would put a underground filter in it, put a small layer of rocks with sand on top of the rocks.
I really like the sand and I want to keep it but do you think the under gravel filter with pebbles and then sand will work without all of the sand just falling through the holes of the under gravel filter?

LOL, no that will not work. Been there, done that and the best part is your under gravel filter will recirculate the sand making a snow globe effect in the corners! I added sand on top of gravel in my goldfish tank and it quickly settle to the bottom and when I siphon it gets sucked up again. The dust you see is either a bacteria bloom if your water has the milky cloudy look there is a fish is rooting around in it. I love the look of sand too, but you have to be careful what kind you get. Sometimes it compacts down too much for planted tanks or other times floats around everywhere. The eco-complete substrates work well, the right consistency. Other types of sand release the silica compounds and cause diatom algae blooms.