ok Update. I've just moved everything out of the 4ft back into the 100 gal. Some of the fish werent too happy about it but im sure they will get over it
I bought the cuytting board material to line the bottom of the tank with. I did not stick a layer of substrate to it liek i was going to do. After i sat the board ( 3 pieces ) in it looked quite fine like that and i thought it was acceptable witout adding the risk of importing toxins with any form of adhesive.
The 4ft is now clean and drained. All the substrate is gone and i am just about to start re-filling it using RO/DO water. It also is now BB and has a layer of cutting board on the bottom.
Im pretty flat otu with work at the moment. Working very long days and not staying at home. Having said that i am trying to do as much as i can to the tanks. This still includes setting up the sump, getting a new Skimmer and plumbing both tanks into 1 system. I need to manafacture OVerflaows and find a way to get them into the tank whilst full. I need to make standpipes and also physically construct the sump. oh.. and if that wasnt enough i have started planning the return manifold
I wish i coudlget you all some pictures and get started on all this but as i said before work kind of inhibits this somewhat. If anyone has any hangon EASY to uderstand overflow/standpipe designs i woudl be most appreciative.