Patchy pigmentation on some Phal leaves

[Fuerte Rav]

Can anyone help me identify what's happening with the leaves on a couple of my phals?
I have 8 phals grown under these particular conditions and it has only affected 2 of them so far. Another 20 phals grown in different conditions (bark media or leca SH) are fine.
So these 2 phals have 1 and 3 leaves respectively that are affected. They are grown in leca in clear pots inside a decorative pot with plenty of airspace between the inner and outer pots. No sign of any pests.
They are in a south facing room but in an area totally screened by sheer curtains. Day temps have been between 20C (68F) and 30C (86F) for the last 6 months, night temps 20C (68F) to 25C (77F). At least one of the patio doors is open during the day and a small window which is also open all night, so there is always airflow.
RH is normally 50/60%. If it drops below 50% I water more frequently.
Watering: these particular Phals are watered every 3 or 4 days. At this stage the roots on the surface of the leca have turned silver whilst the roots inside the pot are still green. If the humidity drops below 50% I water every 2 or 3 days. I fully dunk the pots in water/solution for about 20 mins a time. Once a month it's a Kelpak solution, once a month just plain water. All other waterings contain a very dilute fertiliser.
Fertiliser: 5-5-5 and 0.05% Hierro (Fe), 0.04% Magneso (Mg? label damaged), 0.01% Boro (B). Recommended on label is 20ml to 4L. I use 5ml to 5L.
I still haven't got a proper water report, 18 months and counting ...... and as I spoke about when I first joined OB, my water is desalinated. However, all other Phals seem really happy.

[estación seca]

Your older plants? It could easily be nitrogen, iron and/or magnesium deficiency. All are necessary for making chlorophyll.

5ml of 4-4-4 per 5l is so dilute it's almost not there. There is a fertilizer calculator on the First Rays Web site. You're giving about 36 parts per million of nitrogen once a month. The other minerals are in even lower concentration. A lot of people would use 10 - 50 ppm nitrogen at every watering, or 125 ppm every week to two. If you mixed the fertilizer as directed on the label it would be about 182 ppm. You could use that every 1-3 weeks with your nice warm temperatures.

If it's magnesium deficiency it will take a lot longer to fix. I would suggest, in addition to your fertilizer, using Epsom salts, hydrated magnesium sulfate. Add a large spoonful (about 15 ml of powder) to your fertilizer solution.

[Fuerte Rav]

Thank you so much ES. My brain turns to mush when I try to calculate fertiliser dilutions. I've read Ray's stuff and it makes sense at the time but putting it into practice dissolves my grey matter.

[rbarata]

Calcium and Magnesium for Orchids - St. Augustine Orchid Society

[SouthPark]

Also ----- even though not necessarily the case ----- watch out with the way that the water could/can propagate up the stalk of the phal(s). That is - if the roots are quite wet - then roots could under certain conditions run into issues (especially cold and wet). Or the wetness gets into the crown and leads to something - either of which case could stop nutrients from getting into the phal - possibly resulting in leaf drop etc.

On the other hand - if this is a vitamin/nutrient/element deficiency case - then providing some supplements would help a lot.

[Ray]

That looks like classic underfeeding to me.

If you can get some urea, a foliar spray will help remedy the nitrogen deficiency quickly, but otherwise, just increase the fertilizer concentration, as ES recommended.

[estación seca]

Rereading your post, it sounds like you're using a liquid fertilizer mixture. Are there any powdered mixtures available to you? Liquid forms are a lot more expensive per given amount of nutrients than are powdered forms. Let us know what is available to you and we can make suggestions.

[terryros]

My experience tells me that you have to consider virus.

[Fuerte Rav]

Thank you all for taking the time to respond and offer your thoughts and suggestions.
I've not seen any dry orchid fertiliser here but I'm happy to continue with the current liquid one and increase concentration as suggested.
I've also not seen any Urea products so normal orchid patience will be required.
I've compared my leaves to the online pics of possible viruses and none seem to quite match so fingers crossed it's not that - I'll continue to monitor though - thanks for the warning.
Thanks again, I'll report progress or otherwise.

[estación seca]

Fertilizer used on orchids doesn't need to be labeled "orchid fertilizer." Any fertilizer for other plants can work just fine if the element numbers on the container are correct, and the fertilizer is mixed properly. I was commenting because the very low number liquid fertilizers are extremely expensive compared to powdered fertilizers with higher numbers.