i have my adf's in a 5.5 gal tank. the store i purchased them from told me they can't be in water more than 8 inches high. so i have it filled 3/4 of the way but the current from the filter is too strong from the water spilling into the tank from so high up. is it ok to fill my tank all the way to the top to reduce the strength of the current so they arent struggling to swim? or would that be too high for them?