[pogodzib]

First off, I'd check the silicone to make sure it isn't dried out or cracking. Next, I'd find out if any chemicals, such as copper, were used in it since it can be absorbed into the silicone and slowly leach out over time. After that, I'd clean it out with a 50/50 vinegar/water solution really good and fill the tank outside to make sure it doesn't leak.