Every time they spawn they will learn better ways to care for fry. Cichlids are generally smart enough to learn when something doesn't work... but hiding fry in gravel is a very primal instict for them. I would at least urn the flow off on the UGF while the fry are wigglers (from the time the eggs hatch until the babies are able to swim, which is usually 3~4 days)... that is if I can't talk you into taking the UGF out all together.
I've seen people use UFG on 'bare bottom tanks' and they are fairly effecient (though less than a sponge in my opinion)... and I've seen them used on Community tanks full of fish like Tetras and so forth which produce little waste and produce only small waste... but for Cichlids... there are so many better options I see no reason to use them...
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But again, if your undecided and they lay eggs... just turn the flow off on the UGF about 48 hours after the eggs are laid. This will greatly increase your choances of survival (but won't help against your killer snails

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