Backwashed the Triton II
Next in the continuing pond rehabilitation project...
With some trepidation, we took a weekend to research the pond pump and filter and do the first backwash in years. Of course nothing is labelled, but the piping nicely matched the diagrams in the manuals I found online for the Triton II and the backwash valve. And luckily, none of the valves were stuck.
With the state of the pond -- clear water, heavy organic build-up, and huge algae growth -- I was expecting sludge and grosser from the backwash drain. To my mild disappointment, the water ran nearly clear, with some suspended green and brown bits. We ran the backwash for a minute, until I had the feeling we were just wasting water as it flowed downhill (toward the citrus trees, at least).
While the pump was off, we took the opportunity to check out the condition of the filter medium. Happily, we discovered the old Triton II pool filter is not using sand, as it would in a swimming pool installation. The filter media appear to be 1/2" (or so) ceramic or stone spheres. (I wish I had remembered to take a photo of it, when we drew some up, but we were just focused on the job.)
With no gunky outflow, and no apparent filter media disasters, I suspected the backwash had been a bust. Until I checked out the pond and waterfall with everything flowing again. Water flow is up 300%! By that measure, it was a success.
The placid pool at the top where I was sheltering feeder goldfish had become a swift rapid, which took at least one goldfish over the falls before I could hastily rig up a higher, wider gravel barrier. The waterfall was splashing wider, and the overall pond water level was higher. A parent observed: "Oh, right, *that's* how it used to look." In each pool, the faster water flow carved a path in the sediment on the bottom, stirring up great clouds of muck and turning the water dark and cloudy. (Sadly, this left the feeder fish gasping for air. By the time I had read enough of GW archives to understand what was happening and why, it was too late for them.)
Following the recommendation in the manual, we were very careful to use the air bleeder valve to get all the air out of the system when we restarted the pump. The pressure gauge on top of the filter dropped from 30 PSI pre-backwash to just under 20 PSI immediately after. One week later, the PSI is creeping back up to 27 or so. I suspect we would have to backwash regularly to maintain clarity, flow, and low pressure -- but we've now decided to temporarily drain the pond for other reasons, so I'll post about that in a separate thread.
Below is a side-by-side photo comparison of the flow over the water fall before and after the backwash. On the bottom, you can see the difference in the height of the gravel/lava rock barrier at the top of the waterfall.
Here is a link that might be useful: About the project