What to do when AL keeps re-contaminating itself?

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Hi guys, I'm a bit of a tig n00b but am having problems with something I'm trying to weld on.The part in question is a wood-fired heater for a hot tub.  Moving it around I managed to break one of the mounting tabs and having had a guy express interest in it after I managed to break it, I now need to get the tab welded back on...ASAP!  This thing is made out of 1/8" AL plate and so is the tab that is broken off.  The joint I'm trying to weld is a lap joint in the flat position.My tig setup is a lincoln AC 225 buzzbox with an amp-control pedal added to it via schematics I got off the hobart boards.  Hi-frequency box I built myself, water cooled torch.  Running a 3/32nd pure tungsten, 25 CFH 100% argon, max amps set to 200.Normally I can weld AL canoes with this setup easy, but the aluminum isn't as "dirty" as this heater box is made of.  There is a lot of corrosion on the whole box, so I ground the aluminum shiny about 3/4" around the entire area I'm working on, but I hardly get a puddle going and add some filler and suddenly the arc sounds less smooth, gets more "jumpy" and I see flecks of some black and white crap in and around the puddle I just started.  Clean area thoroughly with a stainless brush, restart arc, lather rinse repeat.  Any ideas?P.s. I don't have AC wave balance on my tig machine but hope to have a machine that will sometime in the next couple weeks.  I would hope to fix and sell the heater box before then though.
Reply:If the piece that you are trying to weld is a submerged part, the aluminum will have absorbed the minerals and chemicals from the water. All you can do is try to burn the stuff out before you assemble them. Butter the surfaces with fill rod, clean it off and repeat. When you are able to make a pass without drawing any crap to the surface, you should be able to weld them together.Castings are even worse. I'll weld oil contaminated parts over water pump parts, etc. any day.Just keep at it.
Reply:You're on the right track, sometimes it takes a few shots to get all of the contamination out.  Not much else you can do except be careful with your amps and only use as much as needed.  Im not sure if your machine has a balance adjustment on it, but if it does try turning it down to 55-60% ENCheck out this thread as well, maybe you can find something useful.http://weldingweb.com/vbb/showthread.php?t=51983Have we all gone mad?
Reply:I would also turn down your argon flow to 12-15 lbs, you don't need that much gas and to0 much gas flow on AL can cause problems with the arc. I know this won't help with contamination but I had the same "jumpy" erratic arc at 20+ lbs of flow.
Reply:Originally Posted by SR20steveI would also turn down your argon flow to 12-15 lbs, you don't need that much gas and to0 much gas flow on AL can cause problems with the arc. I know this won't help with contamination but I had the same "jumpy" erratic arc at 20+ lbs of flow.
Reply:Go see your LWS and see if they stock nozzle flow meters. Most people use them for wire feeders, but they will work for TIG welding as well. You just hold your nozzle vertical and set the flow meter on top. As long as you know your actual gas flow, it doesn't matter what your gage reads. They are handy and a lot less money than gauges. Not saying you shouldnt replace the gauges, but if you have one of these, you can check your flow any time you question the accuracy of your cylinder top gauges.
Reply:That's not a bad idea, but a needle flowmeter just isn't going to give accurate results.  The ball in tube type meter is by far the way to go for TIG.