Ginger bug does not produce enough carbonation

I am using the following recipe to grow an active ginger bug:

2 cups bottled water 2 tbsp grated organic ginger 2 tbs refined sugar

Each day I add 2 tbsp ginger and 2 tbsp sugar to the mix. I wash all my utensils with bottled water before using. I use a plastic spoon for stirring. Temperature ranges between 22 C and 28 C.

After 24h the bug is showing signs of fizziness, but only small bubbles. This doesn’t change significantly after 48h. After 72h it goes flat and if I keep feeding it will eventually develop a slight film of mold on top.

If, however I start brewing the ale after 48h have passed (for syrup I use 2L water, 54g ginger, 273g sugar, 3 lemons, brought to room temp and mixed with 100g ginger bug liquid) it will not develop enough carbonation after 3rd day of bottling. It does have some fizziness but it’s not near to making a “pop” sound when the bottle is opened or have proper carbonation when poured in a glass. The liquid also seems sweet enough, so I would say it is probably not a case of all of it being eaten away by the bug in the ale.

I have tried numerous times and the outcome is the same: either flat bug by day 3 OR not enough carbonation if I use the bug on day 2 for making ale.

What am I doing wrong? Can anyone please help? I have read all sorts of advice and tried to mitigate sources of error having to do with ingredients, so I can’t tell what it is that I’m doing wrong, especially because everyone says this is the easiest recipe to get right :)