It was brought to my attention that I'm posting in the wrong forum with my Tomato disease and so I've reposted it here and referred everyone there to here.
Without further ado . . .

*********************
Plant: Tomato from Seed bought in plant shop in Thailand.
Plant Type: Indeterminate - vining tomato plant of the slicing tomato variety.
Location and Weather: Tropical South East Asia, thought they were started after the rainy season and it's the dry season still.
Watering: went from over watering to now drying out a bit between watering - was every day and now is every 2nd day.
Medium: EWC, Peat Moss or Coco Peat (as available and not quite enough of it) and parboiled rice husks and to a lesser degree crushed mussel and oyster shells and some bubbled rotten green (compost tea).

I got my first ever nice, fairly tall tomato plants growing in my garden in sunny tropical SEA (something like 200km from Saigon). However, first one and now several seem to be turning to ash from top buds or leaves, but in the worse cases also further down the plant (in the pictures it's from the top).

The soil is approximately 40% EWC, 30% boiled and washed rice husks and 30% Finnish peat moss, with some organic fertilizer stuff (fish bits and blended rotted bubbled greens) and some crushed sea shells.
There's Devilish little 2 year old who has been watering them a tad too much, which ultimately killed one plant before I got it stopped and I'm suspecting maybe the remaining plants getting too wet has given them some kind of fungal thing or ?

The plant that was taken out of circulation had the ashen issue to a much further degree, with dropping leaves and it was almost falling over (they're held up by fishing line). I'm holding back on watering and I'm checking the PH value, since the little girl that has been watering them (this has been put to a stop already) was using drinking water with a rather low PH value.

My potting mix consist of rice husks/hulls as a substitute for perlite/vermiculite and I used peat moss and earth worm poop apart from rice husks. The issues with perlite (floats to top, isn't renewable and isn't available in SEA) meant that Rice Husks are much preferred, but as I have to prepare them myself (straight from the rice mill) perhaps boiling them for 5-10 minutes wasn't enough or I need to do more washing and scrubbing and PH neutralization before mixing it in the soil maybe.

Anyhow - this kind of plant disease - I figure it must be systemic and I fear I can't do anything to reverse it. I figure I might be able to slow it down by preventing over watering, but once it's in the plant it stays there. If this is the case, the clones I took from the plants might also be infected! I'll start new plants and a green house that'll be locked (preventing babies, rats and other destructive elements from entering).

Would still be nice to figure out more precisely what ails them though...

I usually let plants go fairly dry before watering, among other reasons the potting soil I make from coco peat or peat moss, with rice husks and earth worm castings, tend to be a bit on the heavy side (haven't got enough of the peat), which also means daily watering will be a problem.
Since I'm in a tropical South East Asian country, I don't have to wait a year, but rather could just start some new ones immediately and I do have 5 clones coming from these plants.

Since I now found this fabled Tomato forum, I will try to make some pictures that encompass more of the whole situation . . .