Leaves of single-stemmed climbing pothos slowly dying, one by one, from the bottom to the top

I have a single stem pothos going up wall, supported by hooks. The leaves on the pothos are slowly dying, one at a time, from the bottom towards the top.

It gets adequate sunlight, but it seems as if it's unable to support the length of its stem and leaves. The leaves are dying, one by one, very slowly.

Routine:
* Watered thoroughly once per week using a BTI/tap water solution to deal with a Fungas Gnat outbreak (yay!)

Notes:
* I have a layer of pure silica pool sand to deal with the aforementioned Fungas Gnats. Info on the sand found here: https://www.coviacorp.com/products/aquaquartz-pool-filter-sand/

 

How old is this plant?
I don't know how long a pothos can keep a single upright stem going, but I will say that it's natural for plants to lose old leaves as they acquire new ones. That's how it works - old material is shed, sort of like skin and hair on humans. You say it's happening very slowly - is it one old one dies for one new one appearing? It's not like a sculpture on which you can add an extension every year, keeping the original bits intact.

Just lift the pot before watering to feel the weight and determine when it really needs water. I remember being told that they particularly do not like to be overwatered. Keeping to a watering schedule even when heat and light conditions change, so water uptake changes, is more likely to cause issues.

 

Thanks for the response! As for its age: that's a tough one, but I'd say at least 5 years old.

It is happening slowly, but quicker than the plants ability to produce new leaves. The leaf growth is net negative for the plant, as it's unable to keep up with the loss of its leaves.

 

My suspicion is that the roots have rotted off, based on the wilted look of the newer leaves and the presence of the fungus gnats. If that is the case, you might not be able to save the main stem. Could probably re-grow it from a cutting of the new end.