I'd use the 1.25" if I had it laying around without a doubt. The only downside I can think of is the small added cost of the larger fittings that would be required to plumb it down at the manifold and pump, but that should not be a big deal.

I am still trying to figure out the best number of turnovers for my small pond as I fight muddy waters. I continue to beIeive that "more aeration is better", but I struggle finding the ballance beteween stirring up the water and maximizing the aeration. I have the 0523 pump and 3 vertex diffusers in my 1/4 acre / 10 foot deep pond which, if all diffusers are set up on the bottom of the pond, can turn it over many many times in a day (7 or 8 IIRC). I have elevated my two deepest diffusers to be about 6 -7 feet from the surface and have a more shallow one at a bout 4 feet from the surface (all 3 feet above the pond floor). This elevated status of the diffusers reduces the turnovers per day and reduces the amount of muddy waters. The system is much bigger than I need, but raising the diffusers off the bottom helps lower the water flow velocities and still conditions the surface. Surface conditioning is a plus, albeit minor, at my small windless pond as it tends to get surface floaties alot. My pond also gets more water throughput because it has an abumdant watershed.

I have considered going to the "set it and forget it" route and just set the thing to run about 6 hours a night starting about now. This gives the pond about 2 turnovers and allows the muddy waters to settle all day long before I typically frequent the pond and want to enjoy clearer waters.

For the last two years, I have watched the air versus water temps. In the spring, I run the air during the warmer hours of the day and as summer comes on, I start to move the runtimes towards the cooler hours of the night. Then back the other direction getting into fall. This, in my rattled mind, helps warm the waters earlier in the year, helps keep it cooler in the heat of the summer, and aids in keeping the water warmer as the year fades. Is it worth the hassle? IDK...it's just what I have done. If I move the runtimes too abrublty, it seems to affect the feeding habits of the fish, but my fish are weak feeders to begin with. I watch the water temps at 18" down from the surface and compare that to the daytime air highs/lows and make adjustments from there. I am seriously considering just going to nightime air very soon for the reasons above.

One thing that I have done to determine the time it takes to turn the pond over is watch the water temps top to bottom. Before the air is turned on in the spring...the water will be warmer at the upper 18" and cooler at the bottom. Gradually bring the air up starting with 15 minutes and doubling every day checking the very bottom temp and 18" temp before and after the runtime. Once you get to the point where the water temp is within a few degerees top 18" to very bottom...your have found your approximate turnover rate. The key word is "approximate" as I am making this up as I go. I will continue to increase the runtime until I have, at least, doubled the "approximate" turnover time just to be safe. IIRC my pond hits consistant temps at the 3-4 hour mark and I am currently running from 9am to 4pm. My pond is looking pretty muddy with all the rains we've had and reducing the runtime and moving it to nights is really tempting...maybe in a week or so...it's going to be cold at nights this week.

With all that said...if I was not fighting murky water, I would run the air as much as I could so long as it did not encourage the 18" water depth to get warmer than the low to mid 80's in the heat of the summer.

Fish on!,
Noel