White mold in s/h

[Buds!]

I have had a great run with my phals in s/h, I am using 'take away' containers and PET cups for seedlings.

However I was shocked today to see that 3 of my phals in the plastic PET cups have fluffy white mold growing near the drainage holes and on some of the Hydroton pellets!
I took out the phal, it has a few new roots, but some of the old roots also had small bits white mold on it.

Can this be caused by the cup being too 'tall'? Therefore restricting ventilation to the water reservoir?

How do I treat this problem? Do I flush out with Physan 20?

Thanks in advance.
Buds!

ps. There is plenty of air movement in my growing room. The ceiling fan is on 24/7.

[Ray]

Are you sure it's mold, and not just mineral buildup?

[DelawareJim]

I suspect it's mineral salts.

I thought the same thing with my first s/h pot; it was only on the hydroton pellets on the surface. When I touched it, it felt a little gritty. So, it's the MSU re-crystalizing on the surface of the pellets.

Mine flushes away with a periodic watering with just distilled or rain water.

Cheers.
Jim

[Undergrounder]

Even if it is mould it's strange that it's white. Does it look cobwebby?

If it changes colour though its definitely a mould.

I'd isolate, sterilise and clean all the affected pots and mediums and repot them. Perhaps you can sit your pots on a little mesh or an upturned pot or something so the bottoms get more airflow?

[Ray]

You also have to remember that there are soluble residues in the medium from the manufacturing process.

[Ross]

Originally Posted by Ray

You also have to remember that there are soluble residues in the medium from the manufacturing process.

Didn't we have this discussion a while back

For what it's worth, I get the same "cobwebby" deposit on gravel in my drip trays from the MSU solution. I agree with the salts buildup.

[quiltergal]

I give my s/h pots a double flush with plain water before the final water with MSU every week. I know it takes longer to water that way, but I'm not seeing any salt build up or mold. Algae is another story.

[Buds!]

Thanks to all who responded!
I have a picture here of the 'white stuff'

Ray: I think you are right, it is probably 'mineral builtup', the pellet in the photo is actually dry, and the white stuff is powdery and hard.

I wonder why the 'built up' only occurs at the drainage holes?
I mist the top layer of the hydrotons everymorning, may be that is kind of flushing the salts away from the top layer?

So, should I just flush all my pots with water?
Will mineral built up harmful to my phals?
Thanks again, you guys are great!

[Ray]

The edges of the drainage holes show buildup rapidly, as that's the one place where a relatively large supply of fertilizer solution comes in contact with the air over a very small area.

First a little buildup occurs, but then it is wet with more solution, which then loses water to evaporation, but is rewet by more, which dries, but is......

[Buds!]

Hi Ray,
Should I do anything about this 'mineral salt' around the drainage holes? Apart from 'flushing' the whole pot?
Do I need to get rid of the pellets with the 'mineral build up'?
Thanks again!