Help please guys !...pictures attached some sort of build up.

[Porsche928s2]

Hi Guys..... I'm Running NFT table with 3" rockwool cubes.
PPM 400 using canna A & B veg nuts.
Water temp 18 - 20c and ph hovers around 6.0. Girls look fine apart from a little nute burn during there early phase.
Over the past couple of days I've noticed a white crystal type residue appear on the top of the cubes.
Would i be correct in thinking this is a salt build up? If not would you guys know what it is and what is causing this issues and how do prevent it from spreading.
I will cover the table once there ready for final positioning but atm exposed to the 600w hps.
Your advice and help would be greatly appreciated as always.
Hope the pic help ....

 

[myke]

Looks fine just some salt,cover with panda film.

 

[Porsche928s2]

Thanks myke, i was thinking as much but always good to get second opinion..... Covering them today,

 

[Johnny Lawrence]

salt

 

[Renfro]

Likely mildew.

 

[Porsche928s2]

What makes you suggest mildrew?, what actions do i need to take to fix this... thanks for your input Renfro

 

[rkymtnman]

i don't think salt either. the dots are too perfectly round. more like mildew/mold. cover up from the light would be where i'd start

 

[firsttimeARE]

Could be salt. Could be mildew. Nothing to be concerned about either way.

The most troubling thing about this is using rockwool

 

[Porsche928s2]

I've covered them up today which hopefully will stop the spread.
Im now thinking mould too as they do look quite formed and consistent in appearance.
Is there some products i can add to the water to help reduce or eliminate these nasty moulds.. thanks for the input guys, appreciate it always

 

[rkymtnman]

I've covered them up today which hopefully will stop the spread.
Im now thinking mould too as they do look quite formed and consistent in appearance.
Is there some products i can add to the water to help reduce or eliminate these nasty moulds.. thanks for the input guys, appreciate it always

mix up a spray bottle of peroxide and water and try to protect the stem while you spray the top of the rockwool

 

[Porsche928s2]

Apologies if i sound a bit stupid but which peroxide is best for this purpose... i have house hold bleach or maybe hydrogen peroxide... pic attached
Thanks for taking the time to help out. Much appreciated guys