I must join those that say it is NOT SAFE.
My tank was just setup about 8 weeks ago( basically 130 gallons of fuge). I just added the first "fuge kits" from various sellers about three weeks ago. These included pods, minibrits, ministars, worms, shrimp, various dwarf hermits and snails. There was Ulva, and chaeto for macros and I also added a few mollies. I already had some base rock and base rubble from the beginning but with no life.
Well....
I saw a flatworm a week ago and then saw two a few days ago. I decided to use FE before I had a problem with them. I read a few posts including this one and unfortunately didn't heed the right advice. amike5 hit the nail on the head.
I ended up only seeing about 6 or 7 flatworms(within about 30 minutes of dosing the FE) which I removed. I also noticed every single snail and shrimp and minibrit I had was out in the open which is very unusual. About two hours later I decided the few flatworms I had were dead and gone. I started carbon and changing water at about 5% every 30 minutes until I had changed about 30%(40 gallons).
The following day I changed another 40 gallons after noticing my pods seemed to be NON EXISTENT and my shrimp were acting "stoned" as amike5 said. Also my ceriths hadn't moved since dosing.
IT HAS NOW BEEN 3 DAYS:
Final death total isn't in, but so far 2 skunk cleaners are dead and the last one is still twitching just a little. Three of four peppermints are dead and the last is also on its last leg. It is totally out in the open kicking around.
I believe every single cerith(at least 15) is dead. They came out in the open within 30 minutes of dosing the FE, turned upside down, and haven't moved since. The sand looks like a warzone of dead bodies.
The jury is still out on the pods, worms and minibrits. I haven't seen a single one in the last 48 hours. The fugeglass that was literally COVERED in pods is now like a graveyard. There is no evidence of any worms or minibrits at all. This is a drastic contrast to the time just before dosing. Also, the hermit crabs seem to be drugged or dead.
What's alive?
The ministars. Or either they died stuck to the glass and haven't rotted yet. But they never appeared to be under stress.
The mollies. Apparently no effect on them.
The nassirus vibex. They haven't missed a beat, in fact I think they have enjoyed all the carnage. They are swarming everwhere.
The astreas. Dont appear to have been affected.
CONCLUSION:
FE killed them. There is no way I can be convinced that I underestimated the flatworm population. NO WAY. This oversized fuge is my only tank and I have spent countless hours observing it. The pod population had just boomed when I saw the flatworm the first time.
Besides I followed the instructions and even went the extra mile in water changes, AND changed the carbon out after about 12 hours and then 24 hours. These animals were all but dead in the first 15 minutes of dosing. They died a slow death over the next 24 hours or so.
I will never use it again. I will try the nudi or whatever.
And to think, when I first read this post, I had hoped I would be coming back on here telling everyone how great it all worked out.
No such luck.