under water gravel filter (UGF) also has its own disadvantages. it works perfect for a couple of months or so with proper water changes and gravel vacuum. But later u need to take the whole UGF and gravel out to clean the poos / debris trapped inside UGF. this is the really headache time .........

too much work, so i gave up UGF..... i got 10kgs of gravel at home from 2 tanks..