12-30-2007, 01:40 PM
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I always recommend staying away from HDpot play sands for the fact the grains can pack so tightly together, under water it's like concrete. Over time as organics break down that become trapped in the sand, water cannot pass through the sand to "wash it". You end up with a nitrite time bomb. Look at sand over time and you'll see black lines or clumps in it. This is usually some type of broken down matter stuck in the sand like compost. Over time you will see large bubbles forming against the glass, these are basically pockets of methane gas, ammonia gas, and nitrite that cannot convert to nitrate.