It comes with the Pan world pump PX 30, which a solid pump but only pumps 288 gph at 30 watts. On a 6x24 body it works but a pump with more gph takes better advantage of virtual height. The PX40 puts out 480 gph for 48 watts. More virtual height for just a few more watts. My little reactor is only a 3.5x12 with the actual holding volume of 3.5x8 and I use an Eheim 1250, 317 gph on a much smaller reactor chamber. Is virtual height important? I think it is, here is a bit taken from JDieck's CaRx page that explains the benefits.
"Virtual height of the media column: What? Well let me explain. Every time the water passes trough the media it is equivalent to having a media column equal to its height. If the water re-circulates five times, it will be equivalent to have a media column five times taller in comparison to a reactor with no re-circulation pump thus achieving a virtual height of five times. A more powerful pump may re-circulate say ten times thus creating a virtual height twice as tall as the reactor with the pump re-circulating only five times.
The higher the virtual height of the media the longer the time the media will be in contact with the acidic water or in other words the longer the retention time will be and the longer the time, the more effective the dissolution and CO2 consumption will be.
Also the higher the virtual height, the higher the water velocity will be thus making it more effective to drive the calcium and carbonate ions away from the media surface resulting in an increased performance.
In summary, a larger re-circulation pump will increase the performance by increasing the virtual height of the media thus the increase in retention time and the flow velocity.
Now hold your horse! This does not mean that installing a swimming pool size pump in a reactor will make it better, of course there are practical and physical limitations to the size of the pump, limitations like wasted power consumption, propensity for cavitation at the pump, vibration, media tumbling and breaking apart, media carry over and so on."
Some people do not see the need, and some do. A smaller pump will work, no question about it, but it may not have as efficient dissolution of the gas, which then tends to collect at the highest point in the reactor instead of being completely dissolved. If the highest point in the reactor is the effluent, then any gas that would have collected there will be exhausted out the effluent, gas that escapes the reactor effluent is wasted.
