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Thread: Aeration help

  1. #1
    Join Date
    May 2014

    Aeration help

    Hi there, im relatively new to air flow /aeration and looking to set up a system asap. I need a little help deciding whats needed if possible.
    Ill need two systems, both ran by Sweetwater s31 blowers. One system will feed one big fish tank (15000L) and needs 12cfm at 40" in a 48'' deep tank.
    In the other system i need to supply 6cfm or more @10'' depth over 24 long grow beds ((18bedsx29')+(6bedsx44')= 786 linear ft total) (stacked 6 tanks high per tower).

    For the second system I was considering my options between a series of medium pore diffusers or diffuser hose. My best assumption is diffuser hose may be better due to its ability to operate at a range of CFM (.1cfm-.5cfm/ft) in case my calculations are wrong or need adjustment. I also need to know how to connect the series of hoses to the blower as their connections are different. Sweetwater s31 Im assuming a series of manifold but i cant tell which suit my interest. As for the first system im confused as to what sort of diffuser to use at all.

    I also need to know how often to add regulators in the system to keep air flow constant.

    Diffuser/ diffuser hose:
    Sweetwater Blower:

  2. #2
    Members David - WI's Avatar
    Join Date
    Feb 2012
    I see you've posted the same question on about 4 different forums without much in the way of responses; so this is just my take on blowers.

    We spent hours & hours combing the performance charts and calculating whether it made more sense to have a bunch of small blowers or a few large ones; and then decided not to use them at all.

    First, they are awful to be/work around. They sound like a jet aircraft that just refuses to fly away!

    We considered putting them in a separate room or building but we still had neighbors and the zoning council to deal with.

    Plus, you have to deal with different pressures if you have different water heights; which could be a nightmare if you have changing water heights in any of the tanks or beds (if the water level goes down, the pressure goes down and all the air goes to that diffuser).

    Also, in shallow tanks you don't get very good oxygen transfer. Fine-bubble diffusers have like 2% oxygen transfer efficiency per foot of depth, so at 10" (of water above the diffuser???) you're getting less than 2% of the oxygen the you're pumping to actually go into the water because the bubbles are not in the water long enough for the gases to transfer in/out of the bubble before it reaches the surface. So 99% of you blower capacity (energy, power) is wasted.

    So then we wasted a lot of time looking at designing & building 16' tall U-tube type units like this:

    Then one day I realized that even though venturi's absolutely suck in terms of flow reduction; it would be cheaper and much easier to run larger more powerful pumps to get circulation and aeration without noisy blowers and diffusers that clog up all the time. And the further the aerated water has to travel in the pipe before it reaches than tank; the more oxygen is transferred to the water.

    So, we ended up with a venturi near the outlet of each pump followed immediately by a static mixer ( that really shreds the bubbles into tiny microbubbles... followed by about 25' of pipe to allow the oxygen to transfer into the water. Then, at the outlet into the fish tank we use eductor nozzles ( so that that every gallon of super-aerated water is mixed with about 4 gallons of tank water before it gets to the fish because we don't want them in supersaturated (oxygen, nitrogen, CO2 etc.) water.

    I'm not saying it's the right way, it's just the way that we decided to do it. Instead of adding a bunch of horsepower in blowers we added a some horsepower to our pumps. Using variable speed drives on the pumps, we can run the pumps at about 70% but increase the aeration (if needed) just by speeding up the pumps... the more water we push though the venturi, the more air it draws in.
    It's all about the fish, dude.

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