3 of my nepenthes, ampullaria, bicalcarata and albomaginata are showing decay on the leaves. Bicalcarata is in the worst shape but it's still alive, it makes a leaf and then it rots. The ampullaria was doing the same but recently the tendril showed signs of decay and I lost it. Now the albomarginata is showing signs also. Had these lowlanders since last summer. The albomarginata was forming pitchers but the lids never opened up. The temp is around 20-23 during day, I keep them on a windowsill and the ventilation is not very great. Could it be some fungus problem? is the temp too low and they are finally giving up? is it a root problem? should i repot? I have a truncata on the same windowsill and it's doing ok. Here are some pictures: http://imgur.com/a/5lAeq