@Aquemini ahh thanks for that, great pick up. I've switched the heat mat off.
Another question, I changed my LED lights that I'm using from el-cheapo amazon one (3 bendy LED strips on a clamp) to a VIPARSPECTRA VA600 on the lowest dim setting. I increased the distance from the light to ~30cm as well, but i guess to your suggestion that this new + more powerful light could be causing it...ill try increasing the distance further tonight.
Thanks guys!