Common sense would (at first) suggest that they only need to be as large as the hole going in to the rotor (inside the pump). But this is obviously not enough. A friend of mine have this problem, he has made A LOT of holes in his background and you would think that it would be more than enough, but he still have quite much difference in the water level infront of/behind the background. His pump is ofcourse quite powerful too (3000 l/h).
I'm asking this because i'm currently preparing a background for montage in my new 540 liter tank. And i don't want to make unnecessary big / many holes in it, it does somewhat destroy the illusion of real rock-wall. If it does matter, these are the specs on the equipment: tank length: 200cm, heigth: 45cm, width: 60cm. Pumps: 2 x 1000 l/h.
There's probably some fancy way of figuring this out using some mathematical formula that one can find using Google. But i thought it was safer (and easier
) to ask any of you guys who might have first-hand-experience.