Is the pump vibrating against the reservoir? If there is hard plastic touching other hard plastic, it can rattle.

Good point, but no. The next time I change the reservoir I'm going to set the reservoir on a rubber mat to isolate from the floor so less hum is transmitted.

If it were in the basement, it would be unnoticeable but this in our home in the "exercise room". I didn't imagine this size of pump - the thing is huge. It appears to be well made and definitely not under-engineered.

I'm going to keep using it for the first crop so as not to introduce new variables but it seems like I may be able to downsize simply because I think they use the same pump for a system almost twice this size and I was wondering if anyone else had tried it.

whats the head of the pump?

im a reef aquarium keeper. the gold standard for quietness is the eheim pump. i use a 1262 for my hydroponics setup (left over, back up pump) as well for my main aquarium, which is in my living room a few feet from my couch. its a bit premium in price, but will last your for years and has excellent resale value.

it puts out a decent 12' of head pressure, enough to run my 16 site setup with 20+ nozzles.

The 85W pump has a 10' head (800 gph), so that 1262 pump is probably too big.

Although they use the same pump design (*see EDIT) for larger systems, probably they are targeting something between 3 and 4 psi for the spray from the irrigation lines. If the actual water flow rate is relatively small and the lift minimal, substituting a significantly smaller pump would lower the pressure of the system out of this range and the spray quality would degrade.

For example, if less than a 100 gph pump could move the additional water the Aeroflo2 36 uses over your 18-system (without spraying), the best you could get away with downsizing would be roughly a 700 gph pump since the more powerful pump is in the design to give the pressure. You can get a handle on this by measuring the amount of water being returned to the reservoir, but more than using one pump size probably went into their design considerations.

EDIT:
Here is a more concrete answer:
The AeroFlo2-18 does not use the same pump as the AeroFlo2-30 & 36. Looks like there are two pumps. The green is 85W described above. The Blue WaterPower 120 is used in the 30 & 36.

The real data are:
WaterPOWER 85 (AeroFlo2-18)
Green case
792 gph; 11.2 feet maximum head, ~82-85W

WaterPOWER 120 (AeroFlo2-30/36)
Blue case
951 gph; 13.8 feet head max., apparently 120 *Watts*

So as originally mentioned you probably need to substitute an ~800 gph pump in the *same power range*; too small will give insufficient *pressure* and too large will possibly be noisier, consume much more power and possibly stress the design with overpressure (or maybe not, we'd have to look at it better to know)

If you google 800 gph, one that comes up is the hydrofarm Active Aqua 800, but the wattage seems low at around 50 Watts. Probably better to stick to wattage when dealing with matching pressure. That same company advertises the Active Aqua 1000 gph which is 92 Watts, similar but slightly more powerful. and with similar head. So probably the gph are exaggerated by different marketers. It sounds to me like the 85W pump that comes with the 18 is typical and maybe even higher quality. So probably the adjustments to muffle vibration noise are a better idea. Here is that mentioned potential replacement pump:

92W 12.13' head ActiveAqua 1000 pump

This post was edited by PupillaCharites on Sun, Oct 20, 13 at 16:31

I bought the Elemental EHP262 and have been using it now for over two months with tomatoes.EHP262 55watts vs 85watts WaterPower.
Pressure in sprayer tubes is slightly less but close enough.
Minimal vibration - just water spray white noise.
No replaceable impeller.
It's much smaller and made cheaper so I doubt it will last as long but I'm happy with the reduced noise and I have Waterpower for backup.

Thanks for the followup so we could all learn more about the limits of what's out there. Looks like your research paid off for you with good results for now, and you're using 70% the power which successfully makes less of a disturbance which is exactly what you were looking for. I'm adding this info for anyone DIYing who is honing in on their pump designs for an Aeroflo sort of design since info on pump selection/performance is not readily available when Goggling.

EHP262
Max. Output: 793 gph
Max. Lift: 9.18âÂÂ
Pressure: 3.94 psi
Wattage: 58W

vs.

WaterPOWER 85 (AeroFlo2-18)
Green case
Max. Output: 792 gph
Max. Lift: 11.2' (spec) (GH promo = 10')
Pressure: 4.81 psi
Wattage: 82W (GH promo = 85W)

The possible confusion of having the lower power (W) pump with the same gph is reconciled technically by two factors, first the working minimum diameter of the pump outlet itself,and second the impeller speed and displacement combination. Most of these pumps get very similar efficiency per watt, so the somewhat lower pressure mentioned is due to a smaller volume of water being moved at a lower velocity. Higher pressure pushes out more water, but requires exponential power to overcome the friction. It is a lot like a cyclist - air resistance is approximated as the cube of the cyclists speed. To ride twice as fast one must overcome eight times the air resistance...ahnd in the process make lots of noise to acheive it... That's why such apparently small gph differences are so easily exaggerated by marketeers without apple-to-apple comparisons of these pumps.

Noise is a major concern with high pressure hydroponics....with pressure comes noise.