Low pH/kH in Water, Low = Bad? Options

[Hamad]

I did a water test and my nitrate level is less than 10. There is no nitrite or ammonia, so the water is perfect and I do around 50% water changes every 2-3 days. There's also good filteration and high aeration and heater set at 30C.

But to my shock, the PH/KH are very low and they probably were for awhile because I did not test PH/KH for months as I don't buffer or try to make any changes to it. KH is less than 3d and the PH less than 6.4.

I did a test to the tap water and the results are very much the same. Does this low (but stable) level of PH/KH could have a side affect on the fish?

I notice that my fish usually show stress (very low energy) even though I feed a healthy mixed diet [different pellets, bloodworms, spinach, etc...] also as I mentioned earlier water is great and temperature at 30c which means fish should be more active than this. Could the PH/KH have something to do with this?

[CyberET]

don't go too high on the KH ;) just follow as what Sabine recommended, and record down/calculate how much u need to raise the KH to the recommended level