Since almost everything in anodizing is a matter of degree, there isn't any "best", everything depends on everything else. This is both a blessing and a curse.
Please define "didn't get the best results" in as much detail as you can. As is obvious, we can't see what you are doing or what your results are.
If a large change in both ASF and electrolyte made a small or no change in the results, this problem may have nothing to do with either.
I know that this is going to require you to do a lot of typing, but it will get your problem solved much faster than having us guess. To get you started, I'll list some assumptions I'm making now about your setup, you correct them:
1. Bath temp. 70-75 deg. F..
2. Al or Pb cathode, at least as large as the work.
3. You are using CC anodizing, or at least really measuring the current.
4. The alloy you are anodizing is 6061 or 6063? We need to know.
5. At 12 ASF and with 1:1 electrolyte, you anodized for 30-45 min., under these conditions, anodizing longer will cause dissolution problems.
6. Exactly what are you using for a rectifier?
7. What is the surface area of the work?
8. What is the connection method to the work? Since you are troubleshooting you should go back to soft Al wire and Al bolts.
9. How are you cleaning and removing native oxide from the work?
10. You have properly measured and mixed anodizing dye; if its red (at least) you did measure and correct the pH.
11. You dyed at 140 deg. F. for at least 20 min. longer doesn't hurt.
12. What is your sealing method?
13. You have sufficient agitation in the anodizing tank.
14. Your electrical connections are good (all of them). I've been a practicing EE for 30 years and I can't tell a good connection from a bad one just by looking at it. Some voltage vs. current measurements would help a lot.
What have I missed?
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