Did the krausen disappear to quickly?

Hello,
Two days ago I made 10 gallons of beer. I pitched a Scottish Ale Wyeast and made a starter. The yeast worked quickly and within 12 hours I had a nice krausen formed.

A day later the krausen has completely disappeared. Isn't that odd? I have two carboys, both are the same. It happened quickly to the first carboy and now I've noticed it also happened to the second one (so the second was slower). I've never used this yeast so I'm hoping it's specific to this strain?

The room temperature fluctuates between 69 and 72, never really dropping below that so I'm a little nervous. I broke my hydrometer today so I couldn't take any readings.

Is this a cause for concern?

Thanks.

I've never used that yeast strain but have had some ferments settle out really quickly. Your temp range sounds pretty close to perfect so I personally wouldn't worry. Are you still seeing action despite not having a krausen? Did you aerate / oxygenate? How vigorous was the ferment for the first few days? How big was the starter?

Not to worry. Krausen size and duration don't impact the final product.