I seem to recall a little while back that a slower flow of water over the screen was now thought to be better for GHA than originally thought and that flow rate guidelines had been revised. Like most things when you are trying to recall where you read it you can't find it or did I dream it?
You did not dream that, but it also wasn't anything that was "officially" revised, if there is an "official" person at all. What I had mentioned in comments somewhere was that the target flow rate of 35 GPH/in was something that is good to shoot for, but that guideline doesn't have any strict adherence requirement or anything. Similar to putting in less intense/quality lighting, you can also "de-rate" a screen's capacity if you run it at a lower flow rate. How much you would de-rate it is debatable, but I'm sure that it's not a straight-line graph. The primary reason I started bringing up using a lower flow rate was for the break-in period. It's definitely a mistake to exceed 35-40 GPH/in with a brand new, bare screen. One reason is due to arcing of the water flow, leaving one end without water (the end near the water source). New screens have no "resistance" to them. As you get some calcification of the canvas, even the part inside the pipe/slot, this tends to cause the arcing effect to be less noticeable. As you get growth filling in the screen, this will also cause the flow to balance out, and you can then increase the flow if you need to. But for the start-up phase, not only does a reduced flow help prevent arcing, but it also helps to prevent new growth / spores from literally getting washed away. So in reality, you can start out with flow comparatively low, like 20-25 GPH/in, and you can leave it there for as long as you need to, as long as you don't use really intense lighting. It's all about balanace - flow, lighting duration, lighting intensity, and delivered nutrients. Once you get past the initial stages, you just have to find that balance point (which will also shift over time as your tank conditions change). One person's balance point might be at a lower flow rate than "recommended"....and that is just fine...
Thanks, Bud and yes that makes sense. What I do when first running a waterfall scrubber is to set the flow so the whole screen is covered then turn it up a little more so that once algae appear some tracking will occur and parts of the screen will not get the flow required. Once I get GHA growing I reassess the flow required. I run a Jebao 3000 pump and started it on 4 lights on the controller. I know have it turned up to 6 lights of the 8 I could run it on.The head of the pump is just 18" max
