My trout have completely stopped eating pellets, suddenly, in late July. Can it be water temps, or? Is this normal?

Yes very likely the water is too warm for them at the surface. What is the temp at the surface when you throw pellets? The trout could have also died if the water in the lower pond area became too warm or the oxygen was lost or dropped below 5ppm in the deep cooler water - one or both. Trout dying do not always float in mid summer.

And they won't be eating very many pellets either.......

In Manchester NH - July is the warmest month, with an average high-temperature of 81.7°F (27.6°C) and an average low-temperature of 61°F (16.1°C). Unless the small pond with brookies has a significant amount of underground spring water flow through I suspect the brookies are struggling to survive in too warm of water. Brook trout have a lower tolerance to warm water compared to rainbow and brown trout. If one has trout in a pond during July-August the water temperature and dissolved oxygen should be tested weekly at surface, 6ft and bottom depths.