GE will never say that any of their products are aquarium safe for liability reasons. As mentioned the GE SCS1200 has been used by an aquarium builder that I personally know exclusively for 15 + years as well as I have used it myself and there have never been a problem. Stay away from products that have mold inhibitors in it as this will kill everything and GE's silicone II probably has chemical in it. GE silicone 1 used to be safe but I do not know for sure if it still is as they may have included chemical to it also.

So the official word from GE is that all GEII silicones now contain petroleum distillates as a mildew inhibitor. Unofficially, this hasn't always been the case. My friend used to be a chemist for GE and he has told me several times now that only the Kitchen and bath version had this. He's surprised that we're even having this problem and didn't know abou the switch. So it seems they've changed it in the last year and a half or so, and this is why so many people have used it in the past without issue.

On all of the GEII bottles I have it says 100% silicone and makes no mention of the 1 to 5% mildew inhibitors. I guess it's too hard to write "95% of this product is 100% silicone". Previously only the GEI and GEII kitchen and bath had the inhibitors; seems like the "premium" line of GEII only now carries his option.

When I chose GEII for my tank I did so for strength and quality rather than price, and on the recommendations from several reefers and a guy who used to work with the stuff. The chemistry behind GEII allows for a better bond to glass and has less tendency for the inside seems to peel away from the glass with age, so you don't get the tattered look some old tanks get. It also has more give to it while being stronger and has better resistance to the elements (ie. Salt water). This formula though evolves ammonia rather than acetate; however, it is "supposed" to cure much faster. It is spposed to be minimum 3 hours to water ready, 8 hours to moderate strength and 24 hours to fully cure. Bare in mind this is not accounting for the evolved ammonia to dissipate. I've seen several threads where people make emergency repairs with GEII and fill the back up with water in 8 hours without I'll effect. Most tanks "should" be able to handle the relatively small cycle caused bathe ammonia is there was some still there. When I built my tank I let it cure for almost a week and a half, filled it with water for 48 hours twice and gave it angood clean... And I still had a problem when I transferred, so I doubt it was the ammonia and likely an effect of the inhibitors. Big tanks probably notice this less due to dilution. Had it been more readily available to me I would have gone with a RTV silicone that was aquariums safe, but since it wasn't GEII was the strongest, supposedly "safe" product available to me.

When I swapped my tank there were 7 other more probable causes for my problems (temperature swing due to a faulty heater, reusing old sand, broken skimmer shaft so only a small back-up skimmer, etc), so I never suspected the silicone. Seeing what is happening in this tank and having got this other bit of info this morning from GE, I am more suspicious of GEII being the cause but bottom line is: it's officially not reef-safe.

The inhibitors may have caused die off of microfauna which may explain the ammonia spike, rather than ammonia from the silicone itself. If anyone is reading this and having problems with GEII, run lots carbon to remove the inhibitors that may be leeching into the water column. The direct effects of whatever was happening seemed to dissipate within a couple weeks in my tank and was just a long road to recovery. They tank is healthy and happy now and the corals are growing like weeds like nothing ever happened, so it doesnt look like there are major long term effects from the silicone (if that was the cause), just an initial hit.

Yeah but before your tank recovered you lost 90% of your corals. That's a though thing to swallow. Oh, and I not a scientist but I am pretty sure the silicone is responsible for what's going on in my tank....there is no other reasonable explanation for it.

Anyway, I finally got home after running around the city all the day picking up stuff that I'll need to shut down the tank and remove the silicone. Wish me luck.

are all your corals ding well now, how longs it been, GE emailed me back and said the Mildew inhibitor in Silicone II lasts for 5 years. Im wondering if this effects the reef. My tanks has also recovered except a couple corals (one acan/one duncan) its been over a month.

I've only ever used GE1 and let it cure for 2 days,zero problems or loses.

I made the swap over in early October to the new tank. The day after the swap I had my blue mille colony die. A few days after that I had a monti cap recede and was gone a few days after. After that I had a smaller tenuis colony start to recede and I lost part of my purple bonsai. My big green pocci had issues before the swap and slowly faded away over a month or so. These big colonies were about 90% of my SPS, though I still had several big colonies left. Other SPS were looking stressed and I had no PE in them for a few weeks but over time they've bounced back and are growing again. Strangely, during all of this my purple pocci, pink lemonade acro, zoas and pavona were unaffected and grew like weeds (the purple pocci has doubled in size since the swap). I even had a bonsai frag from the dying colony almost encrust the entire plug in just over a week and a chalice grew about 50% in 2 months.

Mid November I was correcting the tank for low mag by slowly dosing over the course of a week and a bit (going from 1000 to 1300 ppm over 9 days). Near the end of this I had a bunch of brittle stars "die". Some died, most recovered. I suspect this may have been from dosing with magnesium sulphate heptahydrate (which can anesthetize inverts) rather than mag chloride/mag sulphate. Brittle stars seem back to normal.

I would say it's been almost three months and everything is back to normal except for my duncan and a monti (which is on the mend). The duncan never really opened again and a few weeks back it just died in a matter of days. The monti cap has been looking rough but has been growing; it seems on its way back to health.

Overall, I'd say within a month to month and a half things were more or less back to normal but my nutrients were still high (nitrates ~10 ppm). After 5 weeks of vodka dosing my params are near zero and that alone has seemed to have had the greatest impact. I have full PE on all my SPS and everything seems to be growing nicely. Over the early few weeks of the whole ordeal I had the symptoms of a cycle (diatoms, etc) but never detected an ammonia or nitrite spike despite testing daily starting on day 3, so I was at a loss at to what was happening unless I missed a spike on the very first day.

So the mildew inhibitor affect the reef? Well, as you can see from this thread and yours and my experience, yes. Long term? I can't really say. My new tank now seems healthier than any system I've had before despite a few healing war wounds and the growing pains of a new reef. Over the past 4 to 5 weeks I haven't seen anything that would suggest that it is still having an effect on my system.

Very sorry to know your loss, Daniel. I am wishing you have a best luck this time.

Hey Robert,

Thanks for your encouraging words. I have learned a costly lesson here. Do your own research and never trust anybody entirely.


Thank is being shut down as we speak. I am not going to wait a few weeks hoping that everything will be ok or better than ever.

Wow that sucks , sorry about your corals. I just set up a cube that i re-sealed with black ge silicon 2 and even after compleatly drying out my live rock so i could epoxy it , there was minimal amonnia . I have tried to introduce a couple of sps frags only to have them bleach and rtn though.If ge is really putting extra stuff in there 100 % silicone im p***** how is it 100% if theres other crap in it.

Lessons that I had learned was always costly and followed with painful memories. Anything bad that has happened to you recently, just think it will be left behind this year. The new year comes to you in a few days, I am sure you will be able to set up a beautiful tank again.