2002 Mitsubishi Galant Coolant question

Hoses at radiator and engine block had worn/gotten old, I could see green residue where the hoses connected to engine, and I was having to top off coolant tank every month or so. Had hoses replaced and the mechanic said all looked good (no leaks, pressure was fine, just worn hoses) but when he took hoses off, some of the coolant was gel-like or thicker than normal. I've only used the green stuff over the last 2 years or so. He didn't seem that concerned about it, or wasnt sure what was causing it. He asked if I had used any stop leak I said no. **Any ideas if this is a big deal or not?**

They offered a cooling system flush as part of the standard hose replacement service for an extra $90, but I turned it down. I'm guessing when they put the new hoses on they put some new coolant in there.