Sacrificial Anode to protect aluminum waste tank.

[gimmeagig]

My 1999 CDS machine has an aluminum waste tank. A few years back I read about anodes and i bought a zinc block from a marine supply place, hooked up a copper wire to it and bolted it to the inside panel of the tank.
Over the past few years I have seen that block deteriorate a bit and I'm thinking that it must work.
My tank still seems to deteriorate because I see little pits on the walls inside of the tank and what it dries out there is a white powder on those pits. Similar to what you see on neglected car battery terminals.
I called a supply place that sells anode rods for water heaters and they told me that the anode does not need to be connected to the tank and the more surface the better.
So my questions:
If surface makes the difference and not mass, would a large sheet be better?
Is there a source for sheets of solid zinc, like 12" X 8" maybe 1/2 to 1" thick?
Would it be effective if I just drop a plate like this into the tank and not connected it to anything?
Would that anode plate need to be cleaned periodically to be effective?
Has anybody here tested a system like that on an aluminum tank?

 

[Chads]

It's been along time since I have even thought much about anodes and understanding how the whole electrolis corrosion works but what you need to know is there is different types of anodes out there(material that it's made of) the sacrificial anode must be more coradble than the material it's protecting. So do a little research and find out what works the best with aluminum. Might be magnesium or something else like that. Hope this helps.

 

[gimmeagig]

So does anybody here know if a sacrificial anode has to make some kind of electrical contact with the tank.Or is it good enough to just drop what ever metal I want to use into the tank?
I know it rests on the bottom but if there is dirt between the anode and the tank there is probably no rel metal to metal contact.Right now i have a wire going from the Zinc block anode to the inside bracing of the tank.
Anyway, I listed my specific questions in my original post and I'm hoping someone here might have some answers and suggestions I could use.
And I guess now the additional question is: Is Zinc the best metal to use as an anode in an aluminum tank?