Hi and thanks for the replies. Some details on my tank (rescaped one month ago)-
Tank: 4x2x2 10mm standard glass, braced tank.
Substrate: Plain gravel thats now over 4 years old and full of mulm, clay balls and Seachem root tabs.
Fertilizer regime is EI -
4.5 teaspoons of KNO3
3 teaspoons of KH2PO4
Dissolved in 140mils of distilled water and dosed 20mils per day and 10mils per day of Seachem Flourish and either Seachem Iron or DIY iron mix 2x times per week and Seachem Trace mix 2x per week.
Also for the first time I have used Osmocote 'ice cubes'.
CO2 is administered via a Dupla regulator, Dupla Magnetic Solenoid, Dupla bubble counter, Dupla Reaktor 400, Dupla Drop Checker and a 6kg cylinder.
Lighting: Aquamedic Aquaspacelight 2 x 150w 10,000k metal halide lighting unit.
Filtration: 2 x Eheim 2217 canister filters. One returning through a spray bar and the other through a curved return pipe.
Heater is a 300watt Eheim.
60% - 70% water changes 2x per week, in winter I heat the water in a barrel (4x 300w heaters and an Aquaclear powerhead) with some Prime added, in Summer it's straight out of the garden hose and Prime added to the tank.
I'm thinking I'm going to have to buy/build a better reactor?