I take care of the grounds where I work. Last year they had to have the yard dug up sewer problem, they tore up 75% of it!!! They (the company doing the digging) then hydro-seeded it. 80% weeds/20% actual grass. I used Scott's weed and feed to try to get a start on fixing it. The weeds are winning having been well feed. I should have just wiped out the whole thing with Roundup and started with good seed. How much weed killer can I use, how often, and what do you recommend?