There doesn't seem to be much advice on where to place an airstone. I have read that placing an airstone directly on the bottom of a pond is harmful to a pond. This is because the air diffuser (airstone) creates turbulence at the bottom of the pond which lifts and stirs sediment through a pond.
Many air diffuser systems have a plate which the diffuser is attached to which prevents contact with the bottom of the pond. If it is truly harmful to place an airstone/diffuser directly on the bottom of a pond, it seems that many pond owners make this mistake. Any opinions???
I see no problem if their is a plate underneath the airstone. If the plate is large enough it should keep the air from scouring the bottom. Keep in mind the column flow of air is going up if the bottom of your airstone(s) is pointed in the right direction.
If you're concerned about the stone how about a membrane diffuser that only pushes air up? You can also elivate your stone by various means. Some folk build PVC stands with three way connectors and PVC to elevate their stone up of the bottom about a foot. I have done this.
Float, Look at my FAQ section at
www.cleanponds.com and click on "A word about diffusers" and I cover airstones and rubber membrane diffusers in some detail.You will even find the cleaning instrustions for one of the most popular airstones on the market which some find a problem. Feel free to mail me with any questions anytime , Ted
F-Aerator - To elaborate on Ted's information, I will add some of my thoughts. Typically air diffusers should be separated from the sediments on the pond bottom with either a sheild/plate or with distance or height(on a stand). Diffusers that lay in the bottom sediments, which may be fairly deep, will lift and circulate the light, "fluffy" organic particles on and around the diffuser as the surrounding water is "lifted" or moves into the water column. This can create cloudy and turbid water throughout the pond. Water currents from the aerator will tend to redistribute the resuspended sediments or keep them in suspension until they decompose or settle elsewhere. Duration of this cloudiness will likely continue until all the sediments surrounding the diffuser are pulled or "cleaned away" from around the diffuser. Other factors may also contribute to the long term cloudiness once it develops.
Four sided airstones can under certain conditions expel air bubbles from the bottom of the stone. Although typcially if sized corrrectly with the compressor's air flow the air bubbles are released primarily from the upper surface of the airstone. Bubbles released from the bottom of an airstone lying in the sediments with out a bottom shield will have a tendency to erode the pond bottom sediments and or soils below the diffuser and cloudiness will persist as long as airflow to the airstone is active.
Typically bottom aeration systems that are sized and installed properly will not by themselves make the pond water cloudy or turbid. If a pond turns cloudy after aeration is installed correctly, other factors are usually responsible or contributing to the "problem".
Bill You are correct on the 4- sided airstones. The Great Lakes ALA4GL (picture in Jan/Feb PondBoss pg 35)has a approx 18 X 18 inch underlay for the stones and I have not wittnesed any additional turbitity on these.I would still like to see them 4-6 inches off the bottom. The round Koender type which has a solid bottom and is a different story and is best suited in a 5 gallon bucket to create an updraft. Our Vertex Airstation (pic in action on installation page)is mounted 7 inches above the top of the weighted base and 11 inches from the bottom of base and is designed to sink into muck (organic material) only 4 inches to the lip at the top of the weight box. Something to consider when installing a diffuser into a mature pond bottom.I have replaced many airstones in buckets that fell over at some point even with pea gravel in the bottom of the pail.If one is going to use the airstone bucket method consider drilling 4 holes in the bottom of the pail and inserting 2 pcs of 3/4 to 1 inch pvc to create an X 18-24 inch works.Add 2-3 inches of pea gravel and I would add a float just under the surface so you can find it when it needs to be removed for cleaning. The diffuser must continue to float down as the organic material decomposes. (sorry about getting off the original post)
The PVC X cross "arms" are a very good idea when using a bucket to hold a diffuser. Buckets even with additional ballast weight often tend to tip over due to uneven pond bottom, sloping bottom contours, unevenness of overlying organic sediments AND the tugging or resistence of the incoming airline.
Sometimes the "fluffy" loose unconsolidated organic sediments on a mature pond bottom are 18" to 3 ft thick.
