Yellowing leaves with brown spots

Heres a couple pics of my plant:

The strain is Mandala Ganesh, its in the 3rd week of flowering and it seemed fine until this started happening 5 days ago.

Im growing in soil with a 150 watt hps. I was using flowering nutes at normal strength and when this started happening I switched to fresh water and flushed the plant and have been watering with regular water ever since.

Parts of the plant seem normal, and with flowering I expected the leaves to turn yellow but these brown spots are a mystery and seem to have stunted its growth.

Im pretty sure Im not over watering, I only water when the top of the soil gets dry.

It might be the pH of the water (I havent quite been that careful about that, I do try though so its not just plain tap water) But the soil should offset that though right?

Any thoughts??

Also Ive got a small ozone generator in there to keep the smell down.

I dunno if that would do anything or not.

The plant is not using as much nitrogen as it did during veg, which kept your fan leaves green. It doesn't need very much N during flower. I don't think I would have flushed the soil if I were you, just because the leaves turned yellow with brown spots. Now you've flushed out the nutes that it needs for good flowering to happen. So, you'll need to add your flowering/bloom nutes again. But don't over do it just because you flushed, or else you'll end up in a over-nute situation which does require flushing out the containers.. Good luck to ya. Hope all ends up well...

-S