Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Surface water ought to show gentle ripples. Less than that usually leads to surface scum and reduced oxygen levels in the lower levels.
Below the surface the plants ought to sway in the water. Less than that suggests there may not be a good circulation of fertilizer, CO2, O2 and so on. The plants cannot move to go find what they need, these things need to come to them.
An AC 30 on a 10 gallon tank is at the higher end of good flow, so a sponge over the outlet might help divert some of the flow, but keep working with it until you have it right for your tank. Perhaps a thinner sponge would allow a more even flow, rather than diverting so much of the flow sideways?