as he sais gravel from outside can mess up your ph and kh? and they might have some toxic minerals inside, so i wouldnt recommend it either...ralphinnj said:I would not recommend it. I used some gravel once meant for landscaping, and I had problems with pH in the tank. You can't be sure what is in the stone and how it's been prepared. If it has a lot of acidic minerals, your pH will stay low, no matter how much "pH UP" solution you add. I went through bottles of the stuff to no avail. In addition, my Oscar's contracted a disease from the low pH and died. I know the gravel you can get at home centers is cheap and offers other interesting options, but it is NOT worth the risk, believe me.