The RD3 pump makes adjusting the tuning the skimmer much easier. Increasing the pumps speed/wattage increases the water flow and air volume into the skimmer. This also tends to increase the bubble size. Decreasing the flow/wattage decreases the bubble size while also decreasing the amount of air drawn into the skimmer. The advantage over this approach vs the adjustable volume on the standard Red Dragon pumps is as follows.
It allows for much more flexibility in varying environments. No two tanks are the same as far as nutrients, salinity, temp, sump water level etc. All of which have a direct impact on the optimal skimmer settings. Having control over the pumps flow like that allows to skimmer to be fine tuned much easier for those kinds of variations.
Sump level can have the biggest impact on a skimmers performance and in cases of sumps that are particularly deep, a lower pump speed may be needed to prevent overflows where as a sump that has a lower water level may require greater water flow into the skimmer to keep the foam head up high enough. Tanks with low levels of DOC's also benefit from that kind of control as skimmers in low nutrient tanks have a harder time producing a consistent foam head. Being able to control water flow and air bubble size like that, gives an advantage over the traditional pump that can only be dialed in via the adjustable volute and sump level.
I've used both style pumps. The original Red Dragons with their adjustable volutes on my previous bubble king skimmer and the RD3 on my Supermarin 250. The RD3 has made dialing in my skimmer and maintaining consistency much much easier. Many would think that slowing down the skimmer pump would be counter intuitive but because the bubble size, air volume and water flow into the skimmer is impacted by the pumps speed, it actually works really well for fine tuning. Especially because the adjustments can be made in very small increments. Not only that but because of the differences from one tank to the next, having that kind of flexibility with the skimmer where our tanks setup, nutrients and or sump levels may not be so flexible makes a world of difference in really getting the skimmer performing to the best of it's ability. In my case, my skimmer is in 9" of water which is at the upper end of the range for the skimmer. I found that a setting of about 36 watts out of a total of 50 watts is optimal for my tank. Not only does that pump allow me to get my skimmer dialed in easier but it also saves on power consumption which for me is important as my electrical bills have been known to be off the charts.
Lastly, if for any reason you want to skim really wet or make a quick adjustment, all it requires is a quick push of a button as opposed to tinkering with an adjustable volute that doesn't really give you a good indication of where you are as far as adjustments. With the RD3, you get a number of the display that makes for easy reference when tuning the skimmer or going back to a particular setting.
