dont know what is goin on

[fourkbmx]

i've been anodizing 7075 with no problem for a while, and now i just bought a 6063 tube for testing, and i cant get it right. when i dip the 7075 in caustic soda almost immediately it turns black, but this doesnt happen on the 6000 alloy im working on, is this normal? this is the first time im going to work with 6000 alloys, is there a trick to it?
by 720 rule

.7mil
10amp/sq foot
25 V
50.4 min

my main concern is that im doing something wrong with the volts, i didnt knew that you have to set the volts dependin on the alloy.

[acidrain]

You're OK.
6xxx doesn't smut like 2xxx and 7xxx. You'll still want to give it a quick dip in de-smut though.
As for the volts, those are just guidelines of what you can expect to see. All of the alloys have different voltage curves.
Just set your volts all the way up, and your amps all the way down. Then start by slowly turning up the amps to your target current. The volts will do whatever they need to maintain the amps.