I use algone too.
I use the big bag, because they say you can't use too much, and this way, I have to replace it less often.
Every week I do a 30% water change and flush out the filter and purigen bag. I also notice my algone bag is bloated and covered in slime. I assumed diatoms as well. If you squeeze the bag, it smells like death itself..... I squeeze the bag out, and scrape off the slime and put it back in my fileter....I throw it out and replace it about every 3 months (I use the big bag for ponds).....
I have a bit of algae growning on some driftwood, but it is not much and it looks cool. I have a lot of plants and CO2 injection and my 2 otos keep them clean, I see no algae on the glass under the light or on the walls of the tank (before I used algone, I got enough algae scrapings every week to make a California roll!!!)
In short, I think the slime is OK cause I haven't had a problem.. fish are happy..
So the real question is, Is the algone keeping the tank clean, or now that I got rid of my pleco and got otos, that that's what is working???? Until I use up all 6 of my bags I bought I will keep using it, then I will consider to buy more or not.