I usually only use 1 unless it is a really bright color such as red. I have never had a problem with it bleeding again.
If there isn't much color on the color catcher after washing and I and washing something that doesn't have a lot of bright colors, such as pastels, I have used it again. I have never used it more than 2 times.

I love Color Catchers!!! I prewash all fabric, using Color Catchers. They are especially great with raggy quilts because you don't prewash the fabric for those. I made a raggy quilt using red, white and black fabrics (for an NC State grandson.) No problem at all with bleeding.

I also use Color Catchers in all laundry when there are any colored garments in the load. Has saved many clothes!

If I have a small load of fabric, I put the cycle on med load and I always start out with 3-4 color catchers and a white cotton towel. It lets me know if I need another color catcher. If the towel has color on it, I do it again with a couple lmore color catchers and another towel.

If you are testing new fabric or washing it prior to using it, why don't you test it first instead of just throwing in Color Catchers? I prewash generally so I use a dishpan with the temp of water fabric will be washed in and let it soak app. 5 min and check to see if it is colorfast. I'm sure I have also read on this site about putting a paper towel under fabric, wetting down a small area, and letting it dry. If the paper towel has color on it, plan on using the Color Catchers or treating it with Retayne.

I use 4 color catchers in a large load of new fabric. I have never had a problem with colors running. I also remember hearing that you should make sure you don't throw the color catchers in the dryer with the fabric, and that is what I do. Really don't know whether this is important or not, but being as I have never had a problem I continue to do it. I didn't know that you can reuse the catchers if they are not saturated with color. I will be trying this.

I keep hearing about Synthrapol and Retayne but I don't know where to purchase those two. wondering if someone can give me some suggestions.

Our quilt shops usually carry Retayne, and it is available in small bottles on-line at Joann's, but not in their stores. Not all LQS's carry Retayne. You need to find an open-minded owner who will admit that sometimes even the best fabrics will bleed.

I think it is nice when gifting a quilt to include a couple of Color Catchers in the gift, as well as general washing instructions. If the person uses the Color Catcher the first time they launder the quilt, they will see by the Color Catcher's appearance whether or not they can expect future problems.

I've also tossed 4-5 in and am glad I did. Sometimes I rerun the load with 4 more.

As for prewashing: I have prewashed fabric and still had a disaster because not all the color came out. But that was before I knew about color catchers.

I also use 2-3 for a new quilt ( I never prewash and use a lot of batiks). I also reuse my color catchers if they appear to have not soaked up a lot of color or no color.

In my experience, you can never go wrong using color catchers. I purchased a new pair of black pants and used two in their first wash. Everything was fine. When I washed them the second time, I tossed a couple of color catchers in "just in case." Boy, was it the right thing to do. Both came out almost black -- darker than after the first wash!

Good luck.