It wouldnt be a bad idea to get it clean and then put your rock and media from the 300. Add any new rock sand you want. if you have enough rock/media from an established tank again you shouldnt see a cycle.exactly. so not knowing if he sprayed anything, this is where I'm a bit worried. I mean, I can try again but, if there's something now in the water, and coating my tank... I think I'll totally take it apart, clean it...new sand and then add the rocks from the sump, then 1/2 new and 1/2 from my 300. then I'll just let it sit a week, and then test. sound right? at least it's not rushing and I can just observe
Could you wait sure. You could even add an ammonia source and retest to see how long it takes to turn to nitrate just dont go crazy.