If I may, I would like to add a few comments based on my own experience. I too am keeping a low-tech, low light tank. I lit it with one screw-on compact fluorescent bulb; the tank is a meager 2-gal. It gets no fancy substrates, other than the debris from the snails and fish and what not. It also has no filter of any sort. It has been running for 2 years now, and the water has always remained crystal clear. I also don't do periodic water changes. If anything, I only add water to it, and not take anything from it. The water will evaporate, and it is upon frequent observation I will then decide whether it's time to add more water. You were right in saying in a low-tech tank it is preferable to water change in less frequency. It's total opposite of high-tech tanks, at least in many cases. The reason, I suspect, could be related to what I just said. I think a true low-tech tank is one that gets some amount of natural sun light, if not all. In this way, too, the water will become evaporated after some time. In this way then, it will only become necessary to add more water to maintain the desired water level. The low-light and fast growing plants in the tank will do the rest to keep the water clean and clear. Hence, it is not necessary to change water that often, like once a week. You could also get a Normal Output fluorescent light as an additional lighting support for the tank. This might be necessary as the sun light will not always be shining in the same amount throughout the day. You could make things easier for your sister by using a timer, which you can set the time for the light to go on and off. Definitely very helpful given your situation; less maintenance work for your sister is also a great thing. I am pretty sure she will enjoy this new tank you've set up for her. Maybe you can post some pictures later. Best of luck to you both
Paul
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