I have done a lot of research on this and I find a lot of advice that simply does not work for me. So I am very confused what is causing my high KH values. I have operated planted low tech tanks for years with out too much probelms. I know what to expect and how to fix most any problem but this has me stumped. I moved recently and my tap water turns out has a very high KH value. I did not realize this when I set up my 55 gal tank at first and planted it. All went well at first but I could not get the PH down and soon all the plants died. Here are the values of my tap water GH 30 ppm KH 300+ ppm off the top of the scale PH 8.5 It always returns to this value and will never stay down at 7.0. Now they way I understand it carbonate hardness is also called temporary hardness because it can be removed by boiling. So I tried to boil my tap water. After 30 minutes rolling boil KH still measures 300+ ppm GH, still 30 ppm. I had someone test my water KH and he said the KH value was 680 ppm. Not sure how reliable that test was though. That is what has me stumped. What is in my tap water that can not be removed by boiling that is causing the KH values to remain stubornly high? I also have a water softner on my home water supply and that does nothing to remove this high KH value. But it does get the GH down to around 30 ppm. Without the water softner my GH would be around 450 ppm. I am running another 29gal low tech planted tank at my wifes school and a different water source. That tank has been running now for 2 years plants and fish are doing great after 2 years. That tank has: GH 60 ppm KH 0 ppm PH 6.5 Both my tanks run at about 3.5 watts per gallon for light 6000K 10 hour duty cycle. My home tap water is from a deep well source and has a high limestone mineral content. I am guessing this is what drives up the KH value so high. It also fixes the PH at 8.5. I can add lots of PH down to force it down but it comes right back up to 8.5 overnight. Again boiling it does nothing to the KH value. I guess my only fix would be a RO unit to solve my water problem. Has anyone else run into an issue like this? I would like another option other than an RO unit if possible to lower the KH value of my tap water.