Hi Mark,
by dosing easy carbo you are actually running a high tech tank. Easy carbo is a carbon source and should also be accompanied with appropriate fertilisers to feed the plants increased growth rates. With this in mind a 50% weekly water change is necessary to remove organic wastes from the water column which are detrimental to plant health.
To run low tech you remove any carbon dosing and choose appropriate lower lighting levels. This slows the plants growth rates and results in lower organic waste production which in turn means you can reduce water change volume considerably. The plants may need no additional fertilisers than those provided from fish waste, although some people I believe do add small amounts of fertilisers, especially in low fish stocked tanks such as yours.
Cheerio
Ady
