will a poly filter help prevent ich?

Answer 1

Unfortunately, no. These are a resin pad that you cut to fit your regular filter, and they're treated to remove a variety of chemicals, much as carbon does. The advantage of these over carbon is that the pads start out white, but change color to indicate what's being removed (green=copper, brown = organics, reddish brown = iron, etc.).

Ich is caused by a parasite that can easily get through the filter. The only one I'm aware of that can possibly remove it is a diatom filter (also known as a "water polisher" since it removes much finer particles than any other filters). These aren't seen as much in the hobby anymore, but they still exist. And even these aren't 100% going to cure the ich, because when the parasites drop off the fish into the water, many of them hang out in the gravel, where no filter reaches them.

If you're dealing with ich, it's better to use either aquarium salt at 1 tsp. per gallon or a medication with both malachite green and formalin along with reaising your temperature (slowly) to 86o. The increase in temperature will increase the life cycle of the parasites so they drop off the fish faster and enter the water where they can be killed by the treatment.

See more on these methods in these links:
http://www.skepticalaquarist.com/docs/health/ich.shtml
http://www.americanaquariumproducts.com/Aquarium_Ich.html

Answer 2

good water quality will help prevent ich. A good filtration system will help in keeping parasites and infection down, but will not replace the need for weekly water changes. It willhelp, but it won not prevent ich 100%.

There's a lot of ways to treat and prevent ich though: Quarentine tanks, medication, water/fish conditioners, salt baths, etc... I've also had a lot of success in curing ich by heating the tank up to 85 degrees and keeping all light out of the tank for a week. Ich is a big deal if left untreated, but the occassional ich outbreak can be dealt with. The most important thing is to keep your water quality up and catch it before it turns into a major epidemic.

Answer 3

Simple answer, no. Ich is a parasite and will not be stopped by a filter.