mr.wilson
.Registered Member
I was talking to someone at Avast back when we were considering a Hammerhead needle wheel for the skimmer. I have never used a wiping device, so my criticism is somewhat unfounded, but you know me by now... I think the wiper itself will become covered in muck and become just one more thing to clean.
We have a manual pressure sprayer that came with the skimmer. I have attempted to automate it with a Hayward actuator valve, but my relay wiring skills are weak and the project has dragged on for some time now. Once the valve comes on line, we should be good. The pressure sprayer is located way up in th elid and it still gets caked in skimmate muck. The outer washdown is automated by a simple garden irrigation valve so the outside is nice and clean. We run it 4 times a day for one minute.
My concern with any kind of automated wiper or sprayer device is, where does the skimmate go? In my opinion, most of it falls back into the water column. Some of it is skimmed out, but you would need really aggressive wet skimming to lift those heavy particles. A sprayer removes a thin layer, while the wiper removes whatever is there so it should be run frequently.
There are two issues at hand here; one is to remove the "stuff" that is causing the skimmer to slow down its collection process. This can be hydrophilic agents trapped at the top of the skimmer during feeding, or simply the process of carbon binding to skimmate attached to the riser tube of the skimmer, which brings us to issue number two. The concentrated skimmate in the neck is far more important to export than the tea coloured liquid we dump out of the cup every few days. Manually removing it is the most efficient method because you will remove at least 90% of it without importing it back into the water column. The shortcoming of this process, is objective number one is adversely affected during the time between cleaning the neck.
I'm not sure where the happy medium lies, it really depends on how often a particular skimmer model "goes on strike" and halts skimming. Most skimmers shut down while you feed the tank. This is a nice built-in method of assuring that the food doesn't go right down the drain. This is beneficial as long as the skimmer comes back on line within an hour or so. If your skimmer falls into limbo for long periods of time, then an automated washdown of some sort is the way to go.
The best automated washdown system is simple with just one timer that controls the outer cup washdown with freshwater, the inner neck washdown via saltwater sprayer (or freshwater ATO) or wiper device (the guys at Avast are great to deal with), and at the same time create wet skimmate to expel all the new water and nasty stuff out of the skimmer. You could use a DC pump control or AC pump VFD, or you could manipulate the air intake with an air pump on a timer, or a secondary feed pump. Alternatively, you could use an actuated valve to restrict the water exiting the skimmer, but we want to avoid any devices that will cause a disaster if it should fail.
Our cup washdown is comprised of three pressure sprayers and a garden irrigation timer/solenoid. You can build a system like this for under $100 at your local hardware store. Ours uses municipal water right out of the tap, but you could use a 100PSI pressure tank and RO/DI water like the system we use for the mangrove system.
Periodic wet skimming can be balanced with premixed saltwater top-off for gradual water changes. You can get fancy and use a controller with salinity probes and use programmable logic to control the process (actuator valves/solenoids/pumps on timers). Many people run their ATO right into the sump with no mechanical float valve, which I like to use as a last ditch fail-safe. Why not put your ATO influent on a pressure nozzle and spray down the inner neck of the skimmer every time you top up evaporation? RO/DI water will break down skimmate muck better than saltwater, but efficacy may be negligible for such short periods.
