Question 1

What is the recommended cfm? looking to aerate a 20000 gallon pool to raise ph.

Accepted Answer

A common rule of thumb is that you want to move the entire body of water every 24 hours (the air bubbles move the water). Your 20,000 gallon pool is roughly 2,700 cuft of water so you're going to want to move ~113cuft of water per hour or 1.9CFM. Bubble diffusers move about 4-6 times as much water as the air they produce so that would get you into the .3-.5 CFM range for your pump. That may seem quite small but there are other factors to consider; .3CFM to.5CFM is roughly what you'll need at the output of the diffuser so you'll need more than that at the pump. You'll need to overcome the pressure requirements of your pond depth (air volume halves as pressure doubles) and if your airline run is extremely long/small-diameter the friction of the airline comes in to play as well. The guideline above is just a starting point and since there are many additional minor factors to consider we would advise starting with a pump that delivers >1.5CFM and >3psi of pressure in free state (though there's no harm in going larger). 
 
 We hope this helps and thank you for you interest.
 The Rootscape Team

Question 2

Would this  item do a bang up job in a 150 gallon pond with 25 fish at an average of 5 inches each,pond is 5x4 feet 10-17 in. deepwith a hakko 40pump?

Accepted Answer

I returned my aerator because it was too big for my 3200 gallon pond. They were wonderful about returning it. They said they were making a smaller version which I told them interested me.

Question 3

What is the length of each of the 4 tubes?

Accepted Answer

Each of the four tubes are ~9" long.  Thank you for your interest and please let us know if you have any additional questions.
- Rootscape support

Question 4

Is there a spot to tie a rope?

Accepted Answer

There’s no loop or eyelet to attach a rope. However, you could tie a rope around the base

ASIN	B078RHKJMW
Best Sellers Rank	#51,991 in Patio, Lawn & Garden ( See Top 100 in Patio, Lawn & Garden ) #45 in Pond Filtration Equipment
Brand Name	Rootscape
Color	Original White Air Diffuser
Customer Reviews	4.2 4.2 out of 5 stars (888)
Item Weight	2.3 pounds
Manufacturer	Rootscape Marketing LLC
Material Type	Plastic
Nominal Wall Thickness	0.0625 inches
Outside Diameter	0.38 inches
UPC	689353600787
Unit Count	1 Count

Rootscape Pond Aerator Air Diffuser - Replaces Air Stones For Ponds - Pond Aerators For Large Ponds - Koi Pond Filtration Accessories - Pond Aerators For Outdoor Ponds - Pond Aerator Diffuser

Details

Details

Description

Specifications

Common Questions