Japanese Moss Balls

I have a marimo moss ball in my 55g that is dosed daily with Metricide which is a stronger version of Excel. The moss ball is unaffected as far as I can tell. I've had it for about 8 months and all is well. Go for it I say.

I will admitt hat I bought mine on a whim one day while at the LFS without really researching it. I have had mine for about two weeks in a QT and have noticed that it is starting to turn a little brown on the bottom. Does it have to be rotated?
WP are:
Ammonia: 0 ppm
Nitrates: 0 ppm
Nitrites: 0 ppm
pH: 7.6-7.8
Temp: 70-75 F (temp changes a lot at night)
Light: 1.3 wpg for 9-12 hours a day
Dosed with Seachem Flourish twice a week
WC: 20% once a week with Prime
I want to buy two more and put them in a 10 gallon planted betta tank.

Yes, they do need to be rotated occasionally. I also squeeze it a couple of times when I do a WC.

Excel does nothing to mine, also you do have to either let them blow around near a filter output, or rotate them occasionally... I also do mine at water change. And you WILL have to squeeze them out once in a while, because they collect detritus like you wouldn't believe... I call them sh#* sponges, because that's basically what they are! So remember, squeeze it out like a sponge filter, and give it a spin when you toss it back into the tank.

Moved my moss ball to my five gallon tank and it seems to be thriving. No more brown spots. But Mordalphus is right, the ball collects just about everything that comes near it. It's like it has it's own static cling field surrounding it. Still though, when the holidays are over and money isn't as tight I plan on getting another.