Hi, i have recently purchased a small aquarium of 20 litres. it has a built in light which is 9 watts. would this level of light be adequate for most plants? i will be using ada amazonia as substrate aswell.
This is not necessarily true. It depends on the plant as well as the type of light. One cannot judge merely based on wattage alone. This is only a 5 gallon tank. What type of bulb is it i.e. T5, T8 or incandescent? Is there a reflector? What type of plants do you intend to grow? Will the tank be CO2 injected or possibly liquid carbon dosed?
there is no reflector, its not t5/t8 but one of those small 'u' shaped bulbs. i will be dosing with excel or using DIY co2 instead. will also be using flourish. i plan on planting the following hemianthus calitrichoides 'cuba', monosolenium tenerum, pogostemon helferi and rotala rotundifolia. substrate will be ada amazonia II. im thinking of adding an 18 watt instead of the 9 watt. found a nice clip on one on flebay.
Well, it's difficult to say without knowing a model type or number. I guess I'm not really sure about U-turn bulbs. I guess it is a fluorescent? If so it may very well have similar characteristics of T8. What is the diameter of the tube?
I'm not sure where or how the deception started, but the plants you mentioned, like HC and P. Helferi have a much higher requirement for CO2 than for light. Everyone seems to think they need lots of light, then the plants starts to fail and they add more light which makes them fail even faster. Before you know it the plants disappear into oblivion and it's all because the hobbyist doesn't pay enough attention to CO2 and doesn't realize that the more light that's added the more CO2 is required.
HC and P. helferi are not easy plants specifically as a direct result of their insatiable thirst for CO2, and I perceive that you are following the very same pattern of worrying about light instead of worrying about how you will deliver proper levels of CO2 to the tank. You are much more likely to be able to control the tank with lower light and high CO2 than you are with high light and poor CO2. That's fundamental. These two plants might require both the addition of Excel and the DIY CO2.
It also appears that you intend to add Flourish, which is a trace element, and which is needed in only very small amounts and yet you are completely ignoring the most important nutrients for growth, which are Nitrogen, Phosphorous and Potassium (NPK). You might get away with that at 9 watts but at 18 watts that might be a problem depending on your tap water content, although the Amazonia will help a lot with this.