Gravity-fed vs Pump-fed in RDF setups.

I have gotten a lot of questions from people, who are planning to upgrade to RDFs, about the pros and cons of Gravity-fed configuration vs Pump-fed configuration. I feel like this information is very important when you are planning to incorporate RDFs to your pond configurations. I’d like to share some of my opinions about this topic for the benefit of users who are considering RDFs to make the right decision and figure out what setup would fit into their pond configurations. What is Gravity-fed/Pump-fed Mode? >> In gravity-fed mode, water from the pond will gravity flow (freely) to the RDF first, then the pump which is connected after the RDF, will pump water to bio filters or waterfalls. >> In pump-fed mode, pump will be installed before the RDF. The pump will pump water to the RDF, then water will gravity flow out of the RDF to bio tanks or waterfalls Gravity-fed pros: • Fish waste and debris are filtered out before they hit the pump impeller blades. For me, this is the most important benefit in gravity-fed RDF. • More efficient because the area of the drum mesh being submerged in gravity-fed is generally larger than the submerged area in the pump-fed config. • Less risk of draining out the pond due to overflow as in case of pump-fed when RDF failure and the pump keeps on running. In gravity-fed, the worst case is your pump gets burnt out when your water drops too low, but I rather accept that risk than losing all the water in the pond. A well-designed RDF should have a safety feature to cut off power to the pump in the event of failure. • The RDF in gravity-fed setup is easier to hide. Most of the time it will be under a filter pit or on the ground where you can cover it easily. Gravity-fed cons: • Need to lower the RDF enough to make sure that the recommended water level in the RDF is the same as pond water level for gravity flow. In most cases, it will require digging a filter pit unless you have a raised pond. • Need to have thru-wall/thru-liner bottom drains and they must be large enough (4 inch is recommended) to achieve the required gravity flow. • Cannot use with retrofit bottom drains. Pump-Fed pros: • Works for people who cannot use gravity-fed setup, for instance • People who cannot dig the filter pit to lower the RDF to the recommended level for gravity-fed • People who have retrofit BDs or don’t have thru-wall/thru-liner bottom drains for gravity-fed setup • People who have small 2 inch-BDs which do not provide enough flow for gravity fed Pump-Fed cons: • Fish waste is agitated and pulverized by the impeller blades before going to the filter. Sorry, it sounds gross but when the fish poo is pureed with the pump, even though 70 microns mesh does a good job of filtering out most of the waste, some of the microparticles may still pass thru the mesh and stay in the water column and create more burden for the bio filter. • Less efficient because the area of drum mesh submerged in a normal running condition is generally smaller than the submerged area in the gravity-fed. Typically, just a little more than half of the drum being submersed, for that reason, you don’t normally get 100% of the max flowrate on the RDF. • Serious risk of water overflowing the waste tray and draining out the pond in case of RDF failure and the pump keeps on. This could happen to any RDFs in pump fed mode. A well-designed RDF should have a safety feature to cut off power to the pump in the event of failure. Our RDFs allow users to plug their water circulation pump to the Control box so it can safely shut off the pump in the event of failure. For extra precaution, it’s recommended that users should also install a Safety Float Valve in their ponds to cut off power to the pumps in case water level in the ponds dropping too low. • Since the water output from the RDF in the pump-fed configuration must gravity flow downwards out of the RDF, you will need to raise the RDF position higher than the shower/waterfalls…This means you may need to build a high platform for the RDF which could be difficult to hide and for a large RDF/stainless steel RDF, the weight is significant so you need to prepare for that. For me, with RDFs, I would always recommend my customer to go with Gravity-fed configuration whenever you can. Gravity-fed is more effective, stable and is less risk of draining your pond than in Pump-fed setup.