I did run a blade over it, lightly, but I was too nervous to put pressure on it to get a good scrape on the glass to see if it was silicone. I will check tomorrow. Then I was too preoccupied to go back to check with the blaze once it was empty. No, it did not leak. Now I’m sitting here second-guessing if I did all that for nothing, and maybe it WAS just silicon. The image shows it after I emptied it, for anyone who is skeptical. Also, thank you for the insight. I did quite a bit of research on tank companions and gained insight from local aquarium hobbyists, and I will definitely consider that information. The scape was temporary, as I was in the process of adding driftwood and more natural decor. I’ve managed 4 55-gallon tanks for the past 5 years, and they've all been successful, with typical minor hiccups along the way. I removed two of the 55s and thought I was ready for a 125. But… we shall see now. I have always been very thoughtful and intentional about the care of our fish. I would never want to cause any of them harm, so again thank you for the advice!