[Kuruharan]

Gandalf was not 5'6" but one of the tallest member of the fellowship, making him more than 6', taller than Boromir, taller than Legolas and possibly taller than Aragorn(I don't remember exactly how it is stated).

Ah, well 5'6" was just the random number I happened to pick off the top of my head so you're undoubtedly right about that. Still, the difference between 6' and 20' is tremendous.

This along with any ability to actually grow, there could very well have been some small ability, a Balrog could go from a height of 20 feet to 30 feet. Anything larger and we begin to see some major problems.

I don't think that the ability to have a controlled growth spurt of 10' would qualify as a small ability. I think that even a size change of 10' causes major problems. (Of course, I may be taking a too literal interpretation of your words there. If I am let me know.)

I don't see how Morgoth's and Sauron's lack of ability to change shape and size causes a Balrog to lose the ability - especially since Morgoth and Sauron are known to have dissipated their power into other beings and artifices, whereas Balrogs are not known to have done so.

Remember Balrogs were once Ainu and the ability to change shape was native to them in the begining and the only reason why Melkor and Sauron were no longer able to do so was because they suffered such grevious injuries to their person that they could not easily change their form with out much pain and effort.

Allow me to clarify, I see that I phrased my thought about this incompletely and very badly. I did not mean to say that the Balrogs had lost any abilities because of anything that happened to Morgoth or Sauron. That statement was meant as more of a comparison. The reason why I think that the Balrogs lost the ability to change their forms is because they became, in a sense, trapped in their bodies. They spent so much time in their forms that they became unable to shed it and unable to greatly alter it. Granted, Sauron lost his ability to shape shift in the Downfall of Numenor, but was the fight with Ungoliant the reason why Morgoth lost his? I think that Morgoth's spirit became caged in his body because of his desire to be a visible tyrant on the earth. As powerful as the Balrogs were, Morgoth was a much greater being and if he gradually became ensnared in his form, I think it likely that the lesser Balrogs were similarly trapped.

One sentence that I see over and over again on this issue is the statement that the, "Balrog drew itself up to a great height." This sentence does not mean that the Balrog was able to change his size. Again, the situation needs to be remembered. They were in an ancient dwarven kingdom. The Balrog had been running through mazes of tunnels and rooms that were not really large enough for it. When it got to the First Hall and confronted Gandalf it was finally in a room tall enough for him to be able to stand up straight. Aside from getting relief for it's aching back, the 20' Balrog used this as a means of trying to instill fear in the heart of Gandalf.

My biggest problem with the shape shifting Balrogs is where to draw the line. If you take all the opportunities that the Balrog allegedly had to change forms then he would have altered his shape (counting the size adjustment to enter the Chamber of Mazarbul) four times. This was under stress and fighting through most of that time, and chasing after the Fellowship the time he was not fighting. That puts a rather large hole in the notion that it took a great deal of energy and time to rest before making alterations in the physical form. I just can't see that happening. I prefer to go with the simplest explaination rather than have to conjure up a bunch of different theories and ideas that are not supported in the text.
In this case the simplest explaination is that: the Balrogs were only 15'-25' tall (and I believe that 25' is REALLY pushing it), they could not change their forms aside from perhaps some very limited alterations in size, and they did not look like psychotic black labs with bull horns and bat wings.

And, yes I know that Sauron was able to change his form about four times in the grip of Huan, but Sauron was a greater spirit. That effort left even him completely exhausted and he could not fight. The Balrog was still in full flame on the mountain top and fighting like mad.