Ok, the plan is too strip my tank down this weekend, and put about 12 bags of Amazonia 2 to replace my existing substrat, and of course pull those superb Dennerle heating cables out. But, i have a shoal of mature cardinal tetras and a good few amano's and CRS. I am planning to have the tank back up and running by Sunday afternoon, as we have guests. So, all the filter media will stay, and i will try and keep a couple of 100 litres, out of 720. But is there something about ADA gravel and amonia spikes? Will the fish be ok. Shall i keep the shrimps in my zebra tank for the time being. Will there be algae issues?