Well, I think it is just the same size as the picture shows, about 5cm in diameter. According my past record, this plant prefers medium hard water(about 5to8KH) to very soft water(below1KH) because it will become larger and stronger in th former condition.
The first thing I have to say is that the tap water in Taipei is good for plants on the average, aboutPH7.0 2KH or lower, which might be different from yours, so it is easier for us to preserve species preferring soft water. The parameters of my tanks include two types, one is PH6.5, 0~1KH, to make this, I use the sand without lime (meaning it will not make PH higher drastically) and Co2 fertilizer to lower PH to 6.5 , and remain extremely low KH.
Another is PH7.5 5~8KH(the type I post in the topic), which might be like some of your tanks. In this case I use sand containing moderate lime, the original PH will be over8, about 2KH, when I add Co2 to the water to lower PH , the increasing Co2 in the water will make KH higher simultaneously. The most important of maintaining is that we must keep the lime content within the sand at low level as to avoid the KH increasing too fast because of Co2 adding. The power of imaking the PH higher depends on the content of lime from the sand we use.