I'm sure that I'll have lots of folks telling me I'm wrong on this - but I chose to stick with Baquacil because I didn't want to manage it so carefully (my wife doesn't want to have to deal with it, and I'm travelling a lot).

This is my 4th season with Baquacil in a 17.5K gal pool. Over that time, I've been reasonably successful with only two major problems:
1) started when I accidentally sucked a rag into the pump and didn't realize it for several days, developed water mold (white milky appearance), couldn't see the bottom of the pool.
2) around 1 year later, I developed water mold, couldn't see the bottom of the pool.

One standard symptom of water mold that I experienced is that you can't keep any level of hydrogen peroxide for long.

Both times, I resolved the problem by replacing the sand in the filter (had lots of strings of growth of this bioslime water mold stuff growing through the sand), keeping the shock level around 100, and treating the the filter through the skimmer with around 8-12 oz of floc.

Also, I tend to put the pool to bed at the end of the season with a high level of hydrogen peroxide (150-250ppm) -- this works out as a happy pool with clear water when I take off the cover in the springtime... after I drain approximately 20% of the water, which does give me some water change each year.

This year, when I picked up my supplies, they "gave" me a "free" bottle of sand filter cleaner; I said "what is this for?". Apparently, Baquacil is trying to get people to start cleaning the sand to head off the kinds of complaints that I've seen posted here. As I pondered this, it finally sank in that the dealer had told me all along to change my sand at least two times a season -- which, of course, solves the problem in a different way. This stuff apparently eats / dissolves this crud in the filter through strong acid action; you then flush out the acid onto the ground somewhere where you have put baking soda to neutralize the acid. Which means that I don't have to pull apart my filter and figure out how to get the sand out more than every couple or three years. Worth a try.

SO for the next couple of seasons, I'm going to use the following protocol:

1) keep the water chemistry in shape (check weekly, or after major storms that dump several inches of water).
2) keep the sanitizer, algecide and shock levels in line.
3) clean the sand filter chemically about every 6 weeks of operation;
4) raise the shock level to 150-250 before closing for the winter.

Currently, I'm using the Taylor Biguanide and Hydrogen Peroxide Test Kit (K-1725) along with the dealer's water testing.