GH increased without GH booster
OK so I have been using RO/DI water for the last few months on my two tanks: 36 gallon tropical and 26 gallon goldfish. I was keeping the GH at around 3-4. I went on vacation for two weeks so it had been just short of 3 weeks since the last water change. I found the GH in both tanks was about 10. Nothing was added except fish food.
Can the GH increase almost 3-times just from fish food and fish waste?