Yes, that is the best way because you get a real-world reading. But if that's not very feasible, you can estimate it. Generally you want to use a pump with good head loss characteristics, which means stay away from MJs (cobalt, maxijet) and the smaller eheim pumps like the compact 1000 (I know from experience). Something comparable to a Rio 1100 or 1400 is good - QuiteOne as well. The pumps that are a little "beefier" have better magnet drives and impellers. If you calculate your vertical head, then add 24" to that number, that usually compensates for any loss in elbow fittings and such as well as the head pressure due to the slot with the screen in it. If you use anything less than 3/4" pipe, your loss factor gets significantly increased (add 50%). If you use larger than 3/4", the difference is negligible.
Then it's best to physically measure, the slot pipe will add resistance and this will dynamically affect the head because you are also using it as your return, so if you take the slot off you might get a lot more flow
Am I realize I may have to put some back pressure on the return lines (all have valves) in order to get enough flow to the ats
So I finally got my scrubber together and did some testing. Put flow to it and a nice sheet of water was running over the 8" wide screen. Pulled it out of the sump and put it a bucket to measure flow and to my surprise am only getting 2 gallon/ minute. I am running this off a manifold off my return pump into a 3/8 line into ats. Can I get away with 120 gallon/hr?
The short answer is that you can, it's just important to be aware of the potential risks/consequences That's really low (15 GPH/in) so what you would probably need to do is be very careful on how intensely you lit the screen. With that low of a flow, you might hit a point where the algae is not getting enough of an influx of nutrients (delivered by the water) to keep up with the light you are throwing at it, and if that occurs, the algae could regress into a different growth type - typically a lighter green, yellow spongey growth, or you could experience a rather rare situation I call "whiting" where the algae goes stark white overnight. Then, you probably will have to consider the low flow to be somewhat of a de-rating factor. Meaning, if ideal is 35 GPH/in and you are at half of that, your screen "capacity" would essentially be 50% of the guideline/target. That being said, there are many factors that are very much dependent on your specific set, such as: Overall feeding (type and amount, etc) Scrubber lighting type Scrubber lighting intensity & duration Screen roughness & maturity Tank volume Other filtration on the system Bioload (fish & corals) Water changes Tank issues These all come into play at one level or another
OK. I am going to try at that flow and monitor the ats. The screen is oversized so hopefully there will be no issues.
