Foam inthe float box

[brookledge]

I have a raised flue with a hood and preheater. I keep my hood dampered just a little bit and the sap coming out is 190 to 195. My feed tank is not very high. The bottom is about a foot higher than the preheater and the top of the tank is about 2.5 feet high.
Here is my problem. Before I had an RO everything was fine. Now with an RO concentrating anywhere from 7 to 10% I get foam that just keeps ozzing upwards. So I was wondering if anyone else ever had this happen.
It doesn't react to defoamer like foam in the flue pan
Keith

[Sullydog]

I have the same thing happen when I boil. Just squirt a bit of de-foamed in the box and walk away. I do it about every 30 min or so. The foam doesn't hurt anything.