Mould in propogation

I have a long term problem with yeast type of mold that manifests in my propogation trays.I am a grower of wheatgrass and barleygrass that I grow in trays with soil medium. I was using non hybridised seed like spelt which has a husk still present and the problem was minimal, only during hot humid weather occasionally.
however due to crop failures here in Europe I am back to using the naked wheat grain and the problem is almost uncontrollable.
it starts as a yeasty smell and is fairly imperceptable to the eye and the root growth is good and very healthy but I notice a distinct build up of heat being generated in and around the seeds.
Then a white mold starts to appear together with a slight chlorine like smell. Watering visibly clears up the problem but the smell persists and then when the shoots are 2 or 3 inches tall the mold re appears at the base of the plant throughout the trays. As the plants get taller it becomes grey and very fluffy and can be up to 1 inch high. The mold then turns dark grey to black. I have tried many things and to no real avail.
Any suggestions???

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