If I remember correctly he said that the leaves will become yellowish and weak.
Don, yeah he said it can be supplemented by feeding the plant with calcium rich insects or giving it water with some amount of calcium.
Calcium deficiency typically occurs as chlorosis, distortion, and necrosis of leaf tips on young leaves. Now that I think about it the little lid syndrome maybe a sign of calcium deficiency. Just thinking out loud though.
Has anyone thought about reconstituting the RO water with some raw tap water before watering? This goes back to when I was breeding discus and mixed 50/50 RO and tap to soften water to encourage them to spawn. Maybe in the case of Neps, use 90% RO to 10% tap (ratio can be adjusted based on the parameters of your water supply) and thoroughly flush with pure RO monthly.
Having said that, RO water is not "pure" water so some calcium may pass through.
I have on occasion, but not frequently. Usually I just use ferts. However, I have found that Neps Digest raw egg very well and I may start feeding my neps with raw egg, and throw in some of the shell for calcium. We'll see how that works. I'm not sure if Neps are adapted to absorbing much calcium through their traps though, but it's worth a try.
In regards to little lid syndrome: maybe that's what's wrong with my N. ramispina, though the rest of my neps don't have the problem
Since I only use tapwater on my plants, which contains calcium, I find it difficult to believe that the "little lid syndrome" is caused by this. I have only ever seen it on plants that have been disturbed by either relocation, humidity fluctuations, or irregular temperatures. Some people will say they've seen it when nothing has occurred, but I think they may not be paying close enough attention..
A way to check for calcium deficiency is to look for any small spots of dead cells on the meristem or see if the roots are stunted. Deformation of young leaves is also a symptom, but can very often be attributed to other problems.