I have been growing several indoor plants. My apartment does not gets too much direct sunlight but gets enough indirect light. So I prefer growing plants that need less sunlight. Usually my plants grow slow but do not show much sign of disease or death. Since about an year or so I am facing problem of some plants dieing out slowly. Mostly I was advised to not over water. I tried doing so but without any gain. Rather I felt my plants died more or were shedding more leaves or more leaves were turning yellow / brown. In many cases the plats died from the bottom though the top was perfectly healthy. I felt it might be because of root rot due to excess water, so in a few cases I un-potted them and checked inside. The soil was moist but not too wet. Neither did they smell bad or gave any feeling of wetness in my hand. The soil on top was rather a bit dry. There are enough holes at the bottom of the pots for drainage and the soil is very porous with enough coconut fiber added to it. Apart from this problem some of these plants have also started growing black spots / black tips and they eventually are dieing. This usually happens with Zamioculcas Zamiifolia. Sansevieria leaves slowly turn extremely pulpy and soft and fall apart. Ficus elastica did not respond well from the beginning, leaves kept shedding and out of four plants I had two died in about a month and the remaining two also had their leaves slowly turning black / brown and eventually all of them died. Epipremnum aureum (pothos) is the one that has less problem but it also often faces problem of sudden dieing from the root side. I have tried a lot giving less or no water for extended period of time but somehow the problem is increasing instead of getting less. I have a strong feeling that there is something wrong with the soil. Perhaps some infection. Can anyone suggest, anyway so that I can disinfect the soil. Changing the entire lot of soil is not practical and might still not get rid of the infection. Earlier spraying fungicide (I am not sure what it was, it was given by a local gardener) on the leaves did lessen the black spots on the leaves. But it keeps coming back.