Thanks for your replies, sorry it has been a couple of days - we have been away.
The tank is topped off with fresh, specific gravity checked every other day.
The tank itself has a capacity of around 260 gal, but the hood is very long and due to water quality, I have kept it lower to help with water changes, etc.
I am now looking at changing my substrate from crushed coral to sand. I have a big bucket of live sand and I am going to start at one side of the tank and slowly move to the other side. I'm guessing the process will take around 2 weeks or so as I don't want to stress everything.
I'll change the scape at this time as well, thanks for all of your ideas, you've all been very helpful