How to measure aluminum concentration in electrolyte?

[NeoMoses]

What device would be used to measure the amount of aluminum dissolved in your electrolyte, and where can one be purchased? Is this the main criteria for determining when your electrolyte is 'spent' and needs replaced, or are there other measures as well?

[jtsuttle]

I have the same question so I just wanted to bump it up the list.

[Fibergeek]

There was a thread about this a while back, but I can't find it now.

I'm going by memory now; it takes a dissolved aluminum concentration around 20 grams per liter of electrolyte to make trouble. I remember calculating, that in my 3 gal. setup, it would require anodizing around 160 sq.ft. before the aluminum content got to this level. As cheap as battery acid is and in smaller than commercial setups, it's more practical just to replace the electrolyte before you get near the maximum. Titration is the traditional method of measuring aluminum content, I think there are automated instruments also available now, but in small scale anodizing, who cares? I certainly wouldn't waste the time trying to measure it.

BTW, what you read about some minimum Al content being "beneficial" does not apply in current source anodizing. Dissolved aluminum in the electrolyte decreases (yes decreases) the electrical conductivity of the electrolyte. Current source anodizing compensates for this automatically by raising the voltage to maintain the preset current.

(Edited to add another BTW)

I have caught some flak from a pro for using commercial battery acid and not reagent grade concentrated sulfuric acid, it seems this pro thinks battery acid isn't "pure enough". Being an EE I happen to know that lead/acid batteries react badly to contaminants (wrecks battery service life) battery acid is quite pure by necessity. It's cheap because of the vast quantities manufactured for the automotive industry.