3m was intended for pools correct and it can be used in our tanks correct. Its hard to find...and if im not mistaken it might be getting discontinued (dont quote me on that). It is also a PITA to clean from what I understand. That was one of the selling points to me for the estes...I just dumped it out the bag. I dont know if its your ONLY choices for black sand but I know that the 3m S grade and the estes have a nice rounded uniform shape to the grain size making it look good.
Also I think estaes makes something that is not for fish tanks called medium broadcast sand or something like that. If you call the estes or a distributer they will tell you that the ultra reef sand is used for tanks and has some special coating on it...but the broadcast sand is cheaper...and the person telling me about it also said it was not different and was fish tanks safe for cheaper. I didnt look much into it just in case...but I think they were using the stuff for FW rays and they are very picky about the water. Might be something to look in to too....
Also I think estaes makes something that is not for fish tanks called medium broadcast sand or something like that. If you call the estes or a distributer they will tell you that the ultra reef sand is used for tanks and has some special coating on it...but the broadcast sand is cheaper...and the person telling me about it also said it was not different and was fish tanks safe for cheaper. I didnt look much into it just in case...but I think they were using the stuff for FW rays and they are very picky about the water. Might be something to look in to too....