I've seen reports that suggest that the residue from degraded PHMB accumulates and eventually becomes irritating. So, if you've used Baquacil for 7 years, you've very likely reached that point.

There are a couple of things you need to consider.

First, when you replace your cartridge, you'll want to be sure to get a Filbur or Unicel brand -- or OEM -- cartridge, and NOT a Pleatco or other Asian made replacement. If you'll post your exact filter make and model, I'll see if I can help you find a replacement. The online descriptions can be very tricky, since the people selling Pleatco, etc try very hard to present their products as 'just as good' but cheaper, and in the process, often use some very misleading descriptions.

Second, as Dave noted, draining even an above ground can be risky. If you have a soft side pool (Intex, etc) it shouldn't be a problem. But with a steel wall pool, I would recommend leaving at least 6" of water in the pool. Unfortunately, if you do so, there will *STILL* be a bit of a conversion process.

But, straight chlorine bleach should take care of it. Just use your OLD cartridge, while starting up, and switch to the new one once conversion is complete.