The 'sucking loach' shouldn't have problems due to the sand. The sand will be much-appreciated by your cory and will look very attractive - particularly if you go for a planted set-up. It is also true that waste will sit at the top of the sand as there are no cracks (like with gravel) for it to sink into. This is actualy healthier for your water as it means you will gravel vacuum to get rid of the waste and not have the hidden debris still present once you're done - which would otherwise rot, resulting in nitrAte spikes and causing problems for your water quality and, in return, damaging your fish's health. I would encourage you to only get a thin layer of sand though - prefferably no more than 1" - as pockets of gas can form (caused by bacteria breaking down tiny particles of waste) which, if released, can be harmful to your fish. By keeping the layer of sand thin, the fish and regular maintainance should stirr it up enough to keep such pockets from forming.
However, I cannot help but notice certain things about your stocking that I am not sure you are aware of. Firstly, the 'sucking loaches' are also known as chinese algae eaters. These get to 10" and are aggressive fish, beginning to feed-off other fish (particularly taking the slime coat and eyes) as they mature and becoming especialy territorial to their own kind. Silver sharks also happen to be schooling fish (the minnimum being a group of just 3 due to size and activity levels) which grow to 12" and realy need a 120 gallon tank minnimum - you may or may not have a tank this size but I think it's important to bring this to your attenion. Cories also like to be in groups of 4 minnimum but at least get one more if you don't have room for that many. I should also warn you that angels have been known to eat small tetras such as neons so you might encounter problems once the angel is fully grown. So, what I am saying is that you need to get rid of the silver shark, the aggressive sucking loaches, get 3 more cories, and, possibly get rid of the angel too (particularly if your tank is less than 30 gallons and less than 18" tall). Of course it is up to you whether or not you choose to change your stocking to benefit your fish and you might already be aware of all this and have different plans. None the less, I feel it's necessary to let you know anyway and warn you before it is too late for the fish.