If I place water hyacinths in a bucket of water with Miracle Gro,
1) How long should it sit in the solution?

A few days, up to a week will do.

2) Before adding plant back to pond, should I rinse the roots?
You can if you want. I don't bother to!

3) How much Miracle Gro? Do I use according to label directions?

According to directions on container.

4) Can I do the same treatment with my small Colocasia plants that are in pots? And will it hurt adding back to pond as they ARE in pots?

Colocasia don't require a lot of fertilizer. If you want to give them some, do it at half strength.
Putting the pots back into the pond, with a little MG in there, should not cause a major issue.
"Horton"

I'm curious as to why you would want to fertilize them. We have a 1000gal pond with various plants and goldfish. Last year we bought 4 hyacynths and by September we were "weeding"the pond of them they multiplied like crazy. Three weeks ago we put 2 hyancyths in that have now become 5 and two have flowered with no fertilizer in use at all.

They don't look so good, the leaves are a little yellowish. I had heard they like being slightly crowded, but I was only able to afford one, as the local garden store was selling them for $12.95 each. The pond is new, only been up and running since Saturday, so just 5 days, so seemed to me not much in the way of nutrients just yet. I have a couple people who will be giving me some more plants soon. I am trying to get things in to cover the water as it is in full sun and hoping to head off the pea soup, if I am able.

Holy Cow! $12.95?! I buy them for $2.50. You need to find another source my ponding friend. Of course I don't live in OK so what do I know. Just seems that a $10 mark up is pretty steep. No wonder you are trying to baby that one. I would be too. I wish you the best with it.

Is the little guy getting enough sun? I also live in zone 7 and if put them in the smaller pond just a few feet over they get about 2 hours less sun and they really suffer from it. Vice versa with the lettuce.

That's what I said, and I paid anyway. LOL. Crazy, isn't it? That's the trouble with living in a smaller town and I don't think there is much in the way of pond stuff, except to drive about an hour away.
It is getting full sun, all day. With the limited water plants that's available here, that's why I have been trying to find out more information on the use of 'everyday' gardening plants to use. I'd thought about building a small island to float with the roots in the water, plants on top. But, I don't know which plants would do well, and use up the bad stuff in the water to keep it clear. I'd thought of hostas but they like shade and some of the full sun plants don't seem to be suited for a waterscape. Any suggestions?

I use hosta as pond plants. I put them in a 1 or 2 gallon pot and put it in with the water about 2/3rds up, keeping the crown out of the water. There are many hosta who like sun, they just need to be moist!
Also, there are lots of mail order places with good prices and free shipping. I found this, http://www.pondkoi.com/ has anybody ordered from them?