Want to add a water reserve what size pump?

I have an old model of hydrofarm 6 plant system and wanted to know what size pump i would need so i could attach a 5 gallon bucket for a reserve. Also would need to be able to return the water to the reserve at an equal rate which mine doesnt have very big openings for hoses. Heres some pics of what my system looks like.

a 185 gp/h pump will be sufficient for that gauranteed