Hydroponic reservoir + Clay pebbles covered by some white powder?

Hello, I have been trying to grow in a hydroponic system for a while, but my room last year was not appropriate (basement in England, way too humid and not enough air circulation), therefore making any effort worthless.
Anyways, one of the main problems that would happen last year is now happening again during my first grow in the new house, a white powder-like substance starts showing up around the hole to put the water into the reservoir and on the top clay pebbles inside the bucket. It doesn't look like the powdery mildew I've seen on plants, it almost looks like salt. At this stage I am not using any nutrients, the only thing I add to the water is PH down to keep it under control, but that's it.
Any idea what this is and how can I stop it?
Thanks!

Did you wash and sterilize the clay pebbles? Seeing there you have a seedling, so there shouldn't be any salt buildup yet... So it's prob a mold.

stankyyank said:

Did you wash and sterilize the clay pebbles? Seeing there you have a seedling, so there shouldn't be any salt buildup yet... So it's prob a mold.

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I bought them brand new and washed them all clean. The only thing I could think of is that I have to treat the PH of the water I put in the reservoir cause the one in my house is too high, but there was no way I could fix the PH of all the water used to clean them in the first place...

Are you using hard tap water?

Mildew? Powdery mildew or fusarium perhaps?

Sativied said:

Are you using hard tap water?

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I've used tap water to wash the pebbles, generally I use ph corrected bottled water that I leave opened for 24 hours before putting it in the reservoir, but I did use ph corrected tap water the last time I added water in the system, about 8 litres

Reason I asked it cause I get it too sometimes on pebbles I use as a bed when germinating rockwool and jiffies (so when the taproots pops out at the bottom...). I use nothing but tap water in that situation, which is a little high on Ca. I've always assumed it's like chalk-buildup in a washing machine.

Sativied said:

Reason I asked it cause I get it too sometimes on pebbles I use as a bed when germinating rockwool and jiffies (so when the taproots pops out at the bottom...). I use nothing but tap water in that situation, which is a little high on Ca. I've always assumed it's like chalk-buildup in a washing machine.

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So do you reckon it's harmless for the plant?

It's definitely something in the water from the looks of the drying pattern. GL man.

AllenHaze said:

It's definitely something in the water from the looks of the drying pattern. GL man.

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The only thing that confuses me is that the powder is in places where the water has not been...as in, one of the rubber thingy to seal one of the holes for the pipes has come off, so I'm not filling the reservoir to avoid overflowing water... so there hasn't been water where the powder is showing up

rollthatfucker said:

So do you reckon it's harmless for the plant?

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Well, it hasn't resulted in any problems for me yet with the seedlings so yeah in practice I do reckon it's harmless. But again, that's while germinating. I would be a little worried if I saw that much in my rez and at least would want to to know what exactly it is.

rollthatfucker said:

so there hasn't been water where the powder is showing up

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Well if the pebbles would remain wet they wouldn't dry out to leave a residue (if that's what's going on) and since you washed them they've been wet at least at some point. What's the ppm of your tap? Do you have a microscope?

Sativied said:

Well, it hasn't resulted in any problems for me yet with the seedlings so yeah in practice I do reckon it's harmless. But again, that's while germinating. I would be a little worried if I saw that much in my rez and at least would want to to know what exactly it is.

Well if the pebbles would remain wet they wouldn't dry out to leave a residue (if that's what's going on) and since you washed them they've been wet at least at some point. What's the ppm of your tap? Do you have a microscope?

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Oh yeh, I was referring to the powder in the tank when I talked about absence of contact with water.. The pebbles seem to only be covered in this powder if they're on top, all the ones that get regularly watered from the reservoir don't have the same problem.

Regarding my water, I don't have a microscope and I'm not sure what the ppm is, as I just moved to a new house in a new Country, I just know it's safe for consumption. I do plan on using bottled water anyways, I can get 8 litres bottles from a shop for very little money and I trust it more than the one from the tap

(Check Attached Pic) The air down here (yellow arrow) is going to be much more humid then the air up here (pink arrow). The same thing, I'm sure that is going on with the clay pebbles. The top is drying out, leaving a residue and the bottom is still moist so it is not. What is in this red circle? It looks like residue or sediment, is it just a stain? Is there a similar, white crust on your tap faucet at all?