well you seem to have a number of problems.

1. You are using mineral water. While mineral water does contain calcium and magnesium (I believe) I am not sure if it contains it in high enough amounts that the plant needs.

2. The PH of your water is very low. This may be fine if your soil has a buffering agent in it but without knowing the ph of your soil you want to try to water with something at ph 6.3-6.8 since you're in soil.

3. Your temperatures are on the border of being a little warm for the plants (29C in the daytime). Combine this with your fluxuating humidity and it's sure to give you problems. If you are going to keep it at 29C you should really try to raise the humidity a little. Try misting the plants a few times a day.

Do you have any pictures? Pictures really help alot when diagnosing problems.

Also you really need to be able to test the soil run off PH. This is VERY VERY important.

Good luck :thumbsup: