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Would a Sponge Filter run by a Bubbler be better?
Sponge filters are another possibility and work well under certain circumstances (e.g., nurseries, hospital tanks, quarantine setups). If you want to try them, just be sure to use sponge filters that have no metal components and are completely safe for use in saltwater. Avoid sponge or foam filters that have a weighted bottom (metal) and will rust when exposed to saltwater. Sooner or later they will cause problems in a marine aquarium
If you went with sponge filters, I would also suggest that you add a small powerhead or two to your 30-gallon to increase water movement and eliminate dead spots. But as I said, there are better filtration options for seahorses I think you should consider first, sir.