Acroholic;385317 wrote: What is a "correct" flow rate, anyways? I don't mean that to sound like a smart arse, but most flow rates are pretty subjective.

Example, I have just set up two chillers (one on each of my systems), and found that most people don't use the "manufacturer recommeded" flow rates thru them, simply because the head pressure created by the chiller itself makes it unrealistic. Ask anyone that owns a chiller if they have actually measured net flow thru them, meaning a stopwatch and a bucket. Most folks buy a pump and put it on and are done with it.
You would be amazed to see the actual sized pump you'd have to place on most chillers to get the manufacturer recommended flow rates (real flow rate) thru them. Most chillers 1/3 HP and under have 90 degree blarbs that acommodate 1/2"-3/4" tubing (different diameter plastic on same barb). You can place 3/4" tube on there, but you are only getting flow thru 1/2" ID max, simply because the barb is that diameter.
My 1/2HP chiller has 3/4" inlet/outlet, and with a dedicated Mag 12 and 3/4" ID tubing to and from the chiller, I was only getting actual 360 gallon/hr flow. I'd have had to size up to a mag 18 or 24 at least to get anywhere near the manufacturers recommended flow rates.
The flow rate thru my Calcium reactor is about 50-60 ml/min, which isn't a tax on any pump, IMO. My refugium is low flow, so I set it to a rate that looks decent, but I don't measure it. The valve that feeds a GFO reactor is set to a flow rate where the top of the GFO is moving.
If you run UV inline and need to dose something, just turn the bulb off and you don't need to do anything else. And I don't know anyone that runs a carbon reactor in line with the return. It is always a Tee. And if you need to shut off a reactor connected to the manifold, you just turn off the ball valve that feeds it.