Mr. Cody has been at this for much longer than I, but I can say that my 3 vertex diffusers are set no closer than 3 foot off the bottom of my 10 foot deep pond and I get no thermocline. Water temps have been within a degree or two all summer long from top to bottom.

With that said, the 0523 certainly gives you the ability to experiment going deeper and would be my choice along with 3 or 4 diffusers (9").

My 1/4 acre pond is muddy in nature and has had multiple surface scums this year. I have raised the diffusers off the bottom with no noticeable effect on clarity, but higher diffusers do allow for more surface agitation (and less pump wear -lower operating pressure). The closer the diffusers are to the surface, the more surface disturbance up to a point. I have plenty of water movement to turn the pond over during the night when need be and I get more surface agitation for helping with the floaty stuff. I give this example so that you can see where I have had to experiment with my system to maximize it's effects. 4 shallower diffusers, along with the 0523 pump, will turn your pond just fine and give some assistance with surface sheen while 3 deeper diffuser will maximize the turn overs, but reduce surface agitation. 3 or 4 Vertexs OR 2 Matalas is up to your desires and your budget.

IF you think that you will have diffusers at different depths, you will want to put an air flow control valve on the lines going out to the diffusers. This will allow you to adjust the flow to each line and equalize the boils. If not, the deepest diffuser will get the least amount of air while the shallowest one will boil like mad. Just a foot or two between diffuser depths makes a big difference.

I have only experimented with 3 single diffusers in my pond and don't think dual set-ups are necessary in smaller BOW's. I like the option to space them out for surface effects anyhow. I also like to put one in about 2 feet of water in a corner for the winter in case it ices over for any length of time. Probably not needed in my area, but I'm a dabbler.

Fish on!,
Noel