Hello, I'm starting up a 29 gallon tank. It's my first. I love corydoras and this tank is pretty much going to be built for them. As such, I got a really nice, fine sand: the Estes ultra reef stuff. I've seen it recommended a lot and it feels great to the touch, super soft! But, I can't get it to properly settle for the life of me. The water isn't cloudy, but the sand forms a bunch of balls around air bubbles on the bottom of the tank and they float up when touched (by me, it has no fish in it right now). The problem is, no matter how many times I think I've gotten all the balls to float up and skimmed them out, the second I start to stir the sand a little, hundreds of new sand balls form again and the same thing happens. I'm sure that all the sand has been fully soaked. I've had it for over 2 weeks in water the entire time. I've stirred the stuff for hours, and I've even sifted all of it through a fine strainer to make absolutely sure that no sand in the tank is dry or has bubbles. Even after all this, when the sand sinks to the bottom, touching it forms these bubble balls - hundreds of them! And they continue to float to the top. I've tried removing about 5 pounds from the tank and adding it to a medium sized bucket. I tried getting only this small portion of sand to stop bubbling, but I can't - after stirring, sifting, even after siphoning out all the bubbles resting on the sand, the same thing happens afterwards. I'm kinda stuck. Has anybody had this kind of experience before? Are there any ideas for how to deal with it? Of note, it seems like the Estes sand comes in two brands: the Ultra Reef (which I have) and the Stoney River. The Stoney River stuff seems to be coarser. The guy at the fish store insisted they were the same (but they clearly aren't). Does anybody know anything about this? Maybe I need the Stoney River stuff. Is it ok for corys too? The only real alternative is Tahitian moon sand and that stuff is super sharp feeling. I've heard pool filter sand is good, but it doesn't come in black. Any help would be extremely appreciated. Thanks!