Hi I have been growing two pots of mature sized cobra lilies since March in London and they have been thriving both on my balcony or windowsill, produced half sized mature stolons. But ever since around July the new leafs on the smaller one begin to blacken, then the entire plant begin to soften and collapse. I would have thought that survived the heat wave. Now there is no sign of growing and i can't seem to find pest, which I was thinking it could be spider mites. (above)this is before they started collapsing and dying: new leaves are tall and healthy. I was quite amazed by how fast they grow. (above) this is few days after. I have very occasionally put ice in the water tray, and tried to top it with cool water. I thought I could have shocked the entire plants. (above)These two are the mother plants now, which both have stopped growing too. There was at least two stolons on each plants and they have died too... see picture below which was taken a month ago.