With 13 koi in a 4,500–5,000 gallon pond, I'd focus less on the gallon-based charts and more on your actual stocking level, water temperature, and overall circulation. Those charts are decent guidelines, but heavily stocked koi ponds usually benefit from more aeration than the minimum recommendations.
Medo pumps are definitely proven and reliable, especially if you're looking for something that can run 24/7 for years. I've also had good experiences with linear diaphragm pumps in general, as they're efficient and usually quieter than many piston-style units.
One thing to keep in mind is that air stones themselves don't add huge amounts of oxygen directly—the real benefit is the water movement and gas exchange they create. If your waterfall already provides decent aeration, placing a few diffusers in areas with less circulation can make a noticeable difference.
For a pond your size and fish load, I'd probably be looking in the 80–120 LPM range (roughly 3–4+ CFM total) rather than only 1–2 CFM, especially during the hottest months when oxygen demand is highest and water holds less dissolved oxygen.
I've seen a lot of koi keepers underestimate summer oxygen demand. Fish may seem fine most of the year, then a stretch of hot, still weather exposes the system's limits. Having a little extra aeration capacity is usually money well spent.
If you're comparing equipment, I've heard good things about systems from MidWest Ponds as well, particularly for pond owners who want something sized appropriately without piecing everything together themselves.
My rule of thumb: it's pretty hard to regret having slightly more aeration, but it's easy to regret not having enough when temperatures spike.
Medo pumps are definitely proven and reliable, especially if you're looking for something that can run 24/7 for years. I've also had good experiences with linear diaphragm pumps in general, as they're efficient and usually quieter than many piston-style units.
One thing to keep in mind is that air stones themselves don't add huge amounts of oxygen directly—the real benefit is the water movement and gas exchange they create. If your waterfall already provides decent aeration, placing a few diffusers in areas with less circulation can make a noticeable difference.
For a pond your size and fish load, I'd probably be looking in the 80–120 LPM range (roughly 3–4+ CFM total) rather than only 1–2 CFM, especially during the hottest months when oxygen demand is highest and water holds less dissolved oxygen.
I've seen a lot of koi keepers underestimate summer oxygen demand. Fish may seem fine most of the year, then a stretch of hot, still weather exposes the system's limits. Having a little extra aeration capacity is usually money well spent.
If you're comparing equipment, I've heard good things about systems from MidWest Ponds as well, particularly for pond owners who want something sized appropriately without piecing everything together themselves.
My rule of thumb: it's pretty hard to regret having slightly more aeration, but it's easy to regret not having enough when temperatures spike.
