Downdraft Skimmer Updates
Downdraft Skimmer Updates
As I said in my last post, I would like to see some major research and experimentation done in the area of downdraft skimmers. I think they provide so many benefits at so little cost.
I will get on that soapbox soon. For now, let me report some of my findings, so that it might help others later. My downdraft skimmer experiment has been pretty interesting.
Please keep in mind that ALL of this process was severely hampered by the fact that I came into this with NO experience with skimmers. Yeah, I am a little nuts. And I need to save the $$$.
Chapter 1: The Original Downdraft Skimmer
As I described at the start of this thread, I created a downdraft skimmer for my 29G tank (w/ 10G sump). And it just worked great.
It basically consisted of nothing more then a acrylic box into which the water from my main tank overflow dumped. There was a riser tube for which foam to rise into. And there was an inverted funnel attached to a clear tube that allowed foam to exit the system.
There was, however, a couple of "flaws" in the system. First of all, the way it worked, as you read above in this thread, a powerhead and air pump were required to get foam rising properly. Secondly, the way I attached the drain input, and foam riser tubes to the top of the skimmer caused about a half inch of air to collect at the top of the skimmer box.
On account of these issues, I decided to experiment with things some to see if I could either:
A. Improve Skimmer Production
B. Eliminate the Powerhead and/or Air Pump
Chapter 2: Causing Myself Pain and Agony
Ok. This pain came in two parts.
First, I got some limewood airstones in the mail and tried them in the skimmer box. I removed the powerhead and added just the limewood airstone. Well, the result was that I got foam, but not the same kind of dry foam that was spitting through the tube and creating chewing tobacco spit colored skimmate. I mean the original stuff was dark and nasty. But the only thing I was getting with the new airstone was relatively clear. It still stunk a bit, so I could tell I was getting something.
Anyhow, so I decided to work on issue #2 - the air collection at the top of the box. You see, I had attached the two tubes going out of the top of the box by taking 1/2" slices of PVC couples and glueing them to a short stuf of PVC pipe that was stuck through the 2 holes in the top of the skimmer box. That left a 1/2" piece of PVC/coupling extending down into the skimmer box. Well, that section would catch the air and causing it to build, and the gush, build and then gush.
Apparently, that might have been a good thing in the "get dark skimmate" department.
I THOUGHT that the air collection up there was bad. So I basically used a stick and a half of
two part aquarium epoxy to fill in the space at the top of the skimmer box that was gathering air. In fact, I even "landscaped" the epoxy a bit to sort of make an concave section around the foam riser area. Basically, I wanted to force ALL of the air to go up the tube.
So I got all of this done and decided to try it out. The next week or so was kind of blurry. Basically, I didn't get any quality skimmate until the last couple of days.
I experimented with powerheads... Without powerheads... With airstones... Without airstones.... Every-freaking-thing!
In the long run I have settled with the powerhead (maxijet) in the box upside down. I have it situated so that when the water/air bubbles rush into the box from the tank overflow, they fall directly onto the powerhead intake screen. This causes the powerhead to suck in the bubbles and chop them up wonderfully. I also have a limewood airstone in the skimmer box, pumping some pretty good air in as well.
And for the last couple of days I have been getting better skimmate. I still have not got the nasty dark stuff that I got at first. However, I have been getting sort of a coffee to waterred down coffee colored skimmate.
Analysis
First of all, I am sure the axiom applies here: If it's not broke, don't fix it. However, in the interest in the continual improvement of this hobby, I am glad I played around and have made these varied mistakes.
First, I suspect that the air section at the top of the skimmer box was actually a GOOD THING. Before I added the epoxy, foam would leave the box as it was very solidly propelled upward by the gurgling motion. The gurgling actually created quite a bit of force, sort of more "selectively" ejecting foam from the skimmer.
Now, with the epoxy, there is a CONSTANT gurgle going on that basically causes more regular ejection of foam. While this is still putting out good skimmate, and maybe just as much organic matter, it comes at the cost of losing more water from the tank.
As for the airstones, powerhead, etc...
First of all, let me note that supposedly a tank with flow on the order of 1000+ GPH should be able to successfully use a downdraft skimmer with no extra airstones or powerheads required. This, of course, is the real coup here - no extra pumping, heat, or power required for skimming.
With my small tank, however, something more was required.
The best discovered I made was that instead of putting a cheap walmart airstone in the powerhead input screen, the powerhead input should simply be pointed up. After all, the drain is causing plenty of air to enter the system - we just need to use that air more effectively.
Limewood airstones, of course, do create good fine bubbles. Not all are created equally, however, as one of the two brands I tried created pretty large bubbles. Could have just been a fluke or something.
I suspect if I hadn't added the epoxy, I could eliminate the powerhead and allow the gurgling to provide the extra force required to eject foam well. As it works now, the airstone really helps the system to a nice tall head of foam.
Another quick comment. Dugg suggested, while chatting one day, that the foam/skimmer output may have simply been disturbed by the curing of the aquarium epoxy. He relayed some stories about painting a house and having his skimmer stop working for a couple of weeks after that due to stuff in the air.
Where To Next???
First, I am leaving the current skimmer box alone. It's working and, despite my desire to get this downdraft skimmer thing perfected, I REALLY do need it working on my tank.
So I am probably going to get some more acrylic scrap from the LGS (Local Glass Shop...
) and build another couple skimmer boxes. One I am going to build exactly like the first. The second, I am going to build like the first to start out, and then I am going to cut some teeth or holes in the PVC pipe/coupling sticking into the skimmer box from the foam riser tube. I am wondering if something like this might be some sort of a compromise between the gurgling and the current setup. If all else fails, it should probably be an easier way to recreate what I have working now, without using all that epoxy.
I would also like to experiment with some powerheads of different strengh. Right now I am using a Maxi-Jet 600. I would love to see how stepping up and down a notch or two would change things.
Request for Help, etc
First, if anyone with REAL experience with skimmers has any comments, input, criticism, etc, please speak up. I would love to hear your thoughts.
Secondly, I would like to see some more people experimenting with this idea. Downdraft skimmers are good for our tanks. They take less power to run, skimmer a higher percentage of the tank water, and are just all around awesome. I think that a real contribution to this hobby could be made by experimenting around with these enough to figure out how to make them work more easily. I think, in the long run, that these could be trivially simple little items.
And they'd save a whole lot of money, too...
Perhaps sometime I will write my thoughts about this a little more intelligently then just saying that they are "just all around awesome". But I do need to go now...
Thanks for your time and energy!
