So last night i took some pics,and i also worked out a estimated flow of water. I have a est. 860l of water flowing into my sump, my tank's dimensions are 1.8*600*700,of which water level is 600,i also have about 40kg rock (of which 10kg is baserock),and i have a 2cm layer of sand for substrate. Lately i am having GHA problems,mainly due to my own neglect,and changing the substrate from crushed coral to sand(which i did too fast). i tested the water at my nearest lfs, die visdam, the first test i've done i saw some ammonia,nitrite and very high nitrate 50mg/100l. Second test,no ammonia,no nitrite,still nitrate is very high,50mg/100l. Which it boils down to is,that when i started my dsb,i used reggies playsand,about 15cm deep. i seeded it,but no discolouration in the bottom layers. I removed some sand from the bottom,and guess what,the sand was a bit on the dry side, which led me to the conclusion that very fine sand in a deep layer do not allow for water penetration in the botton layers, as i found only the top 5-8cm was wet. The sand in my DT,are showing lots of bubbles beneath the surface,unlike my dsb. any comment on this,coz i'm a little puzzled,thiking of starting a dsb from scratch,with the addition of a ATS,which is 90% complete. Here's a few pics,just struggling to upload