i observe a strange thing.

when my co2 is in good level in my tank, if i turn on my filter to create water flow inside my tank (not surface water movement), even slow water movement, i will see very little bubbling from my plants. but if i turn off my filter and let the water stablized for a while, i can see my plants start bubbling (chains of bubbles coming out from leaves). if i turn on filter again, after 30 seconds, the plants stop bubbling again. i am very sure that it's not my water flow blow away bubbles so that i couldnt see. because even slow water movement will cause the plants stop the bubbling effect. if plants are still bubbling in that way, i am sure i can see it clearly.

how to explain this? is that because my plants like slow or not moving water environment? i always hear that water movement is important for plants but why even very slow water movement stop the plants from bubbling?

thanks.