Ah, now we're talking colours (colors!) so we can almost see what we're talking about without photos!
The white line is more than likely to be calcium/mineral deposits because you water with tap (fawcet!) water which is hard?
(Okay, so I'll stop with the english translation, it's beginning to annoy me too!)
Do some of your leaves have a slight, hardly noticeable white edge to them, particularly those you've had a while? This is also from mains water spray, running and remaining on the tips of the leaves, evaporating and building up a fine deposit after time.
It's said that this long term hard water does no good for orchids because it clings to the roots preventing them to function properly.
I suppose a test would be to select your newest orchid (with no white line) and only water that one with rain or distilled water, see what happens. No white line, it's your water - white line, it's probably the pot!
So don't worry Oldguypops, you're NOT going mouldy just yet!

Pals

Actually, I don't have hard water. I use Detroit city water which is quite good (100 ppm) after I let it sit for a couple days. And I guess the growth isn't white, it's more like light gray.

Do you still think it might be calcium?

Hello again Chris!
Only 100 ppm?, that's very good, enviable even, I don't think you'll have many worries with calcium.
Have attached a photo of one of my terra cotta-pots, the markings are a familiar sight to everyone, even patio pots get the same marks.
My water is hard, you can see there is algal growth at the base where most of the water collects inside after watering, I've attached the photo regarding the original post and to identify whether the green algal growth is the "mold" we are talking about on s/h pellets. The "white line" is a different matter and as it always appears above the algal waterline, I believe this is not mold but a "scum" of various contaminants sitting on top of the waterline and being absorbed through the porous sides of the pot over time (think about the ring around a bath if you hadn't washed for a month!) or a harmless reaction to water from the pot itself, even soft mains water contains some chemicals.
Unless its a pointer to something like calcium which could cause a problem, (and we know it probably isn't in your case), then I wouldn't lose any sleep over it.
100 ppm eh? hmmmm.....that's worth considering a move to Detroit!

Pals

Yep, those are obvious calcium lines.
Mine are not like that. I'll get a pic on later tonight.

Thanks

That white line you have can be a build up of salts . So you might have to use less fertilizer. I fertilize every time I water , but at a lower rate this seems to help/

I was 95% sure they were calcium marks but I deal with my problems by going into a total state of denial......that is until some-one brings me back to reality....thanks a lot Chris ;) !
If you're not putting anything nasty in (unlike me - calcium), then I can't see why anything nasty should be coming out but yes please, pictures are always interesting!

Pals

Many thanks for your view Des, but I'm sure it's not salts from fertiliser, people talk about fertilising their orchids weakly weekly or every other week or even monthly.
I can talk about fertilising mine in six month stints minimum (yes, my head is hung in shame as it should be :blushing: ) which makes me believe it's just a manifestation of whatever goes into the pot, harmless or harmful. Water may go in sparkling clean but think what that media must be like after 6 months or 1 year!

Pals

Just a thought, some years ago I bought some hand made clay pots to plant miltoniopsis , the plants took an instant dislike to these pots and i soon noticed a white powder covering the outside of the pot. It turned out that the person making these pots mined the clay from a dry river bed very close to a salt works !!!. So your problem could be the pot!

Here are some pictures of what I have on my pots. As you can see in the third picture, I am able to wipe it off with my finger.
It sure looks like mildew or mold to me. :yikes:

Any thoughts?? :hmm

I have a similar thing happening to a certain set of pots I bought. When kept constantly moist, these pots develop the whitish stuff on it, and sometimes it turns green as well. It also doesn't smell too great. I have a feeling it's to do with the pot - I think some pots when fired are done so a certain way, or perhaps there is something put into the clay to discourage algal/mold/mildew whatever growth. Pots that don't get the treatment end up looking like this. I water all my plants the same way, and fertilize the same way, and yet only the plants in one particular set of pots gets this affliction.