This works well, but over time the sand will become inundated with gravel. After flushing out the sand darters, simply siphon out the old sand and gravel and replenish with clean sand. A whole sand tank will be easier to maintain, but various factors should be taken into consideration. Undergravel filtration is virtually out of the question. However, an outside power or canister filter will adequately keep the water clean, but be sure the intake stems are well screened.
Sand darters are very skinny and can fit into some surprisingly small openings.
They also do not function as the best filtration medium. On small aquariums, a sponge filter which is cleaned on a regular basis will suffice. Additional aeration should be provided if there is little or no perceptible current circulating through the aquarium. Sand tends to compact itself. The sucker's feeding activity will assure the sand gets churned over and will effectively scavenge uneaten food.