Thanks to Ceg4048 I stand corrected regarding the water changes reason, I really believed that we must do it to nutrient build up, but we must do it to keep the water clean of detritus and organic waste. So in theory if one halved the EI dosing on a tank and didn't do any water changes for a month, but had a large external filter, not much problems would be encountered, right? Reason I am asking is that I am going away for a month, and it would be tricky to ask someone to do water changes on the tank, it is easier to just leave food, dosing and lights on automatic. I could always decrease the light period and stop dosing altogether, mimicking a winter period for the plants. How do you sort it out when you go on holidays? Don't want to come back home with my plants all messed up.