For 29 gallon one powerhead is enough for maintaining the flow of water in the aquarium.
As the 29 gallon size in medium size and can be well controlled with one powerhead.
For 55 gallon the Quietflow Power Filter are recommended as it combines ultra-quiet operation, industry-high flow rate and enhanced filtration which are necessary for maintenance of aquarium.
The reef tank needs regular cleaning to save it from dangerous algae. The rocks are mostly suffered with these algae with the passage of time.
http://www.m-tech.com.au/caravan/caravan.php