I am usually giving advice but today I need some.I have been keeping fish for many years and consider myself wise at that but the plants drive me nuts some time.I am tried of putting them in and at some point pulling them out and going and getting more.I do have plants that live a very long time and do well for months but then one day something happens and they start dying.I would like to get a grip on this.So he is my situation I have a well planted tank that has been established for some time(about a year)It has been very stable and maintained consistently(water changes,lighting filters)The ph is usually 7.0 solid and temperature at 78 degrees.The only changes that I have done is I added a lava rock and been using a diatom filter once and a while.I have been fertilizing with flourish liquid and some root tabs.The tank is if anything under populated Now last week I noticed that my Amazon sword were getting small holes in them(which indicates potassium deficiencies).I did a ph test and found my ph around 6 ,I did a 1/3 water change and fertilized.Now today they are worst so I did a whole bunch of tests,here are the results temp 78f ,0 iron,ph 6.4, gh 2 drops (very soft),kh extremely soft water,0 ammonia,CO2 18 drops 36 ppm,0 chlorine,0 nitrite.Can someone please tell me what I should do to correct this?I have read lots of pages on the web and don't know what I should do.Could the diatom filter be making my water so soft?My tap water is not.The swords are old plants and I hope not to lose them.Any suggestion will be appreciated.Thanks