Yellowing leaves on Monstera, Philodendron, Anthurium

[Ale_V]

Hello everyone,

I am quite new to this forum so I hope I post this in the correct section...

I'm looking for advice because many of the plants I keep in my "greenhouse" (a small room without windows, only artificial light) have leaves with yellow edges that often dry out and turn brown.

Most of the plants are Monstera (I’ve attached several photos) that I grow on moss poles, as well as some Philodendrons. The biggest issues are definitely with the Monstera. Recently, even one of my Anthuriums has shown this issue, but on one of the newer leaves.

The yellowing pattern is always the same: the edges of the leaves start to yellow and then move toward the center, turning brown and crispy as they worsen. It always begins with the leaves closest to the base of the plant and then progresses upward along the stem.

I started growing these plants 10 months ago, from small plants about 5 cm tall. Some have now reached 3 meters, others around 2. In some cases, I’ve performed the usual operation of cutting the moss pole in two and repotting the lower part to allow the plant to continue growing on a new section of pole. Often, in these cases, the leaves near the base start yellowing within 1-2 weeks, even though the plant is perfectly rooted into the moss pole itself.

As for the greenhouse conditions, the daytime temperature is around 25°C, dropping to 23°C at night, with a humidity level of around 90%. I’ve attached a precise graph from the past week (the drop in humidity in the graph is because I had to leave the door open for a bit to water the plants.)

Ventilation is provided by four 120mm PC fans placed in various areas of the room, running 24/7 to keep the air in constant gentle movement.

The light is artificial, coming from 4 LED panels (3000/5000K + IR + UV + Deep Red), positioned at various heights to keep the light as even as possible. The lights are on for 12 hours a day, with a range from 7200 Lux (128.3 μmol/s/m² —> 5.53 DLI) down to 1300 Lux (23.17 μmol/s/m² —> 1 DLI), with the plants arranged according to their needs. Beyond these light levels, the plants start to lower their leaves.

I water about once a week using only RO water with:
* Plagron "Silic Rock" (NPK 1.5 - 0 - 1.7) 1ml/L;
* Plagron "Ph Plus" (to adjust the acidity of the Silic Rock), as needed;
* Plagron Terra Grow (NPK 3 -1 - 3) 5ml/L;
* Plagron CalMag (NPK 5 - 0 - 0) 1ml/L.
* Additionally, once a month I add 1ml/L of iron to the solution.

The substrate in the pots is a mix of:
* Coco Bark -> 1
* Classic Orchid Bark 6/9mm -> 1.2
* Pumice 6/9mm -> 1
* Zeolite 6/9mm -> 1
* Fine Vermiculite -> 0.5
* Perlite -> 1
* Coco Coir Powder -> 0.5

I've tried everything I can think of to figure out what the issue could be, but I'm still stumped. If anyone has any ideas… I’d be grateful for any advice!
Thanks!