Thanks for the reply! Now I am really nervous about the readings... because I can't afford RO/DI system. I may be reading it wrong... I use dajana strips for ph, kh and gh (3in1) and the colors don't match very well. I took a photo of my test strips. I lost the manual which I believe said that you need to wait a minute or so for the ph result, but I am not entirely sure (so I will describe all stages). I tried testing my tap water and tank right now. The tap water test is acting differently than all of my other tank test strips ever did (ph - at first second is yellow, minute later pink, and brownish yellow when dry ; gh - very dark brown at first and yellow when dry - all my other test strips kept most of the color even when dried out).
Now the test strips show different ph for some reason? I tried all my 3 tanks the night before and all showed less than 6.4 right away (yellow) and managed to reach barely 7.2 (orange-ish with perhaps a tint of pink tone in the middle) in the next minute or so (and they have always showed the same result since I got the tanks).
Now both tap water and 1 of the tanks showed very pink tone - so maybe around 8 (pictures were taken earlier before that color change and don't show the color). Can time change results maybe? I usually do all my testing in the evening when lights are out. The pictures don't capture the color of ph part very well.
KH is the same as always for both tap and tank water - baby blue that isn't even one of the possible colors. Possible colors go from light green to greenish blue... So I'm guessing even more than 20 then?
GH is reddish brown in both... perhaps a bit less than 28?
So it seems my tap water is the culprit? I tested my sand with vinegar and it didn't do anything. In just one of the tanks I put cattlebone for snails but all my other tanks show the same results so those can't affect it. The cuttlebone is for rabbit snails that seemed to have problems with their shells, but that might be just from falling down onto the sand. I have driftwood in all of my tanks, plants, some rocks (vinegar tested) and that's all. So no plants for me...?
Except for the ph, the colors in the picture match reality quite well. The weirdly cut strip is my tap water, the straighter one is tank water.
Definitely get a proper test kit. The strips are good for checking things at a glance but are not great at precision work. You need a liquid test kit. They are not terribly expensive and at a minimum you need a gh/kh test kit.
If your water really is that hard it's not that you can't grow anything, but that you will be severely limited in what will grow in your water. You will want to look at plants that can grow in both freshwater and brackish water I suspect.
Ro/di is the obvious choice if you want to open up your options. I haven't looked too much into that myself but I have seen advertised units for around 200 dollars. So something to save for if needed. Hopefully it's not necessary, to find out... Test kit.