I tried few styles ... just to share ...
Used 4 inches of the smallest grain sand that I can find in KL (about 5mm) with plenum system. Used for > 2 years with great success. Great water quality!! I only need to clean the front glass of my tank once a month!!! Problem: water column tend to have "dust" floating in it. I think it is from the dirt on the sand. Also, 4 inches of sand + 2 inches of plenum = 6 inches!!!
Moved house, so removed plenum and re-used sand. Bad move ... the sand was full of waste, so, without plenum, system crashed!!!
Removed ALL sand, and kept sand-less tank. Water is good but not great ... but no floating "dust" in water. I have to clean the front glass of the tank once a week. But, saved 6 inches at bottom!!!
Going to move house again soon, and I plan to get very fine sand (2-4mm) for the bottom. With such fine sand, I cannot put in a plenum. However, only need 2-3 inches at bottom!!
Conclusion ... The plenum REALLY works for me. However, using a deep sand bed WITHOUT a plenum is not conclusive, so will give it another try again!!
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