interesting observation re:air blower

[Michelle Silva]

I finally bought an air blower (WW-39 from AES) ..those who know me here, know how much I resisted this..I had good growth rates in the winter with just splashing, but with the high temps and much slower growth rates I was getting I finally gave in! Not happy about it being an energy hog in my opinion (330 watts)..but I got it all plumbed in yesterday..it was really simple and pailnless,lol..went fairly quickly.

I noticed something very strange..I took a DO reading this afternoon and it read only in the mid 3's in the raft tanks! However, it read 19.3 in two of the fish tanks that had the most fish and there isn't any air stones in there! What kind of saturation is that?? I've only just started using the DO meter, but it's really easy so don't think there was anything wrong with the reading..I', going to calibrate it again,but just did it yesterday.so that shouldn't be a problem.. There are 30  of the 6" air stones from (AES) in the 39' troughs and the DO actually tested lower then it did before we added them...very strange. The water temp did rise to about 85 degrees today!

Geez, I am definitely not investing in a water chiller. I did consider burying hundreds of feet of tubing to cool the water,.just not motivated to do all that at this time,lol..

[David Hart]

Wow, congrats Michelle. That's a nice blower. 330 watts seems like alot, but your getting a heck of a lot of air in return. Maybe after another day or two...the DO level will be more consistant ?

My buddy and I are getting ready to buy a blower also....Did AES help pick the blower (size) and the amount of air stones ?

Which DO meter did you get ? Do you like it ?

Again, 'congrats'......your going first class now   :-)

[Michelle Silva]

LOL, thanks David..yeah for the cost of the blower (around $250) and the amount of air it produces,it seemed the best deal. Until we can muffle it a little better, my husband asked to shut it off at night..so we'll after it's running continuously.

AES guys were very helpful w/ specing it out.. think it s/b pretty much the standard 1/2 cfm per 4'x4'..They had also recommended the 9730 (small green 50 watt air pump) for the fish tanks w/ add'l 4 more 6" air stones..which I did order, but after seeing and hearing this monster of a blower, didn't hook it up yet, want to try to aerate just w/ diverting some over from the blower first..don't want to be overkill and waste energy. Using/consuming more energy in our household is bothering my sustainable thinking..but realize there are pros and cons with going for high production.

i asked our local County Extension AG agent to get it..we have a good relationship..he was stopping by as he was very interested in learning more about aquaponics. I was not interested in getting one personally, but had mentioned to him it would be very helpful to monitor. It's an "Extech" Dissolved Oxygen meter".

[Ryan Chatterson]

19.3ppm is impossible with ambient air. I would try to re-calibrate your meter.

[Michelle Silva]

ok, Ryan..will do.

 

[David Hart]

Did AES give you one of their little yellow rulers ? On the back, it has a chart showing water temp and saturation points. Ryan is right...with your water @ 86 degrees the DO saturation point is only 7.5

 

They must of figured you needed the diaphram pump for the 'depth' of your fish tank(s)....since blowers normally don't pump very deep.   Maybe you could build some diy airlifts, if you only want to use the blower..

Wow, that's pretty cool, that you got someone else to buy a DO meter, that you get to borrow. we need a 'green' smile face..lol.

[Michelle Silva]

I didn't get one of those rulers..

I would have to learn more about air lifts..not too familiar with them.

Technically think our tax dollars are paying for it...I believe the county ext agent's job is to help small farmers..

[matthew ferrell]

For most DO meters:

Turn it on and wait 15 minutes.  This lets the thing warm up.  It should stabilize at a single measurement, or at 100% saturation.

Calibrate it following the instructions.
If it is an optical DO meter(ODO) just put it in, if it has a membrane system it is important to move it around in the water.  The membrane meters actually consume oxygen in the water to read it.  So if you leave it in place it will consume the little bit of oxygen around it and read really low.  Sometime the movement in a fish tank can be sufficient and that might be why you got such different numbers from plant tank to fish tank.   I would however move the meter in both tanks.

Ryan is also correct that 19mg/l (aka ppm) is impossible without blow O2 through the water.  However you mentioned saturation, and percent saturation can be anywhere for 0-100.  So the question is what were you measuring?

By the way, this is more of your tax dollars at work, well actually someone else's, as I am a state extension agent as well(WV).

[Chris Smith]

Michelle, do your troughs have much of a sludge layer? When I first added my aeration the extra movement of water stirred up the sludge for a while. This slightly mucked up roots but it was only once. I believe this extra O2 and water movement caused a lot of organic material in the sludge to decompose faster than it would have by just sitting on the bottom.  Within a week the plants in the troughs were growing MUCH better. After about a two weeks most of the sludge had changed after lots of decomposition. I do not like to remove the slubge because it holds many micro organisms and in an important part of the ecosystem.

[TCLynx]

Yea, adding air can stir things up and until that brief extra BOD (biological oxygen demand) has evened back out and the system caught up you may see some strange readings too.

But as the guys said, warm water and dissolved oxygen saturation is relatively low so unless you are adding in pure O2 somewhere or using some pressurized means to inject oxygen under pressure you are not likely to get over the level on the chart.  When I get home maybe I can scan the chart and post it.

[Michelle Silva]

Thanks for all your responses..  good points to consider.

Matthew, thanks for the info re: DO, I have used it a few times now so kind of familiar with the basics of how to use it. always move it in the water. I was measuring DO level (in terms of % of air), hhmmm, so not sure about saturation..  The directions state that needs to be recalibrated if not in use for  a few days.  I've done this before..we were away for the weekend, I have not had a chance to recalibrate and try again... great to hear of a state extension agent interested in Aquaponics.

I'll let you all know what I find.

Chris,yes, there is some sludge getting stirred up,..yeah, I bet it does decompose much faster : ) The plants do seem to be growing better, but I was just starting to see pretty good growth before getting the extra air..so hard to say if it's a HUGE difference just yet. 

I'll have to check on the amount of sludge there is tomorrow.  There used to be a whole lot in the past..I was battling oak leaves falling into the troughs before and I was taking them out, but other then that I tend not to take out much sludge... I haven't had that issue for a while now that the leaves are fallen and there's shadecloth up.  

matthew ferrell said:

For most DO meters:

Turn it on and wait 15 minutes.  This lets the thing warm up.  It should stabilize at a single measurement, or at 100% saturation.

Calibrate it following the instructions.
If it is an optical DO meter(ODO) just put it in, if it has a membrane system it is important to move it around in the water.  The membrane meters actually consume oxygen in the water to read it.  So if you leave it in place it will consume the little bit of oxygen around it and read really low.  Sometime the movement in a fish tank can be sufficient and that might be why you got such different numbers from plant tank to fish tank.   I would however move the meter in both tanks.

Ryan is also correct that 19mg/l (aka ppm) is impossible without blow O2 through the water.  However you mentioned saturation, and percent saturation can be anywhere for 0-100.  So the question is what were you measuring?

By the way, this is more of your tax dollars at work, well actually someone else's, as I am a state extension agent as well(WV).

[David Hart]

Hi Michelle, How's the DO doing now ?  Well, I hope