For an arrow what ever substrate you use dosen't really matter, since he will never be forageing for food in it.
As far as cleaning it I have rays so they stir it up, if you don't gas can built up underneathe the sand until it is established in the tank for awhile. So if you don't have a fish to stir it up just do it every so often for about 3 months. For me to get out debris I just siphon it off the surface of the sand with some tubeing.
Also depending on how fine the sand is it can get sucked up in the filter. I have fine sand and I get lucky and don't get much in them but I still do none the less. I have heard people saying sand ruins filters but I have had it for a long time and if that was the case I don't think so many people would had sand.
What you have now is fine unless you are opting for sand and want to do the work of changeing the substrate.
If so what I did was found a sand that I liked and that was worth all of the effort of takeing out my garvel, which I had mor than you. I started out and cleaned the gravel the best I could, and the I scooped it all out. So then that is done.
Next take whatever sand you buy, wheter it says washed or not on the bag you should still rinse it off to get out all of the dust and smaller paritcles. I just put as much as I could carrin in a 5gl bucket and just rinsed it with the hose until the water ran clear. Then repeat as nessecary.
Then when you have that sand clean just take it to the tank and take a cup or small container and slower pour it out onto the bottom of your tank. Get as close to the bottom as possible.
Just do the last two steps until you have as much sand as you want in your tank.
But again you don't really need it for your aro unless you want it.