i just defeated the dreaded fungas gnats

I now learned that mulch is not good medium it like resort for pest. well I was battling with the gnats for like 3 days they got really bad so I went out and got neem oil spray, I used it as directions told me but it didn't do much cuz I think I waited to long the infestation was too large. but I then got idea when I was ironing my cloths I took my iron and went and pluged it up and took my pots of soil and took out the first 2 inchs of soil on top layer and threw it away and then I started to iron the soil my idea was that I would burn and kill all adults and larva and it worked like charm killed every single one. but then few days later there back but just see like one or two just flying around I try clap them or sqush there not in soil. so I now been ironing them when I see one flying around. but now I don't see the fuckers in soil anymore but I do see them flying around. I been using neem oil at lights out every day now just try keep them at bay is there any methods to prevent them or just keep them away from my roots. pls any thing this kinda getting annoying I don't want them to multiply any more I also got cup vinegar and soap too trap them.... will the neem oil keep them away how long to use it say to use everyday? I also read that is I put sand on the top it keep them from laying eggs. is this true. and if so could I get sand from my local beach and start bond fire and heat the sand and put it in metal bucket thing and put it on hot coal will this kill all the bugger that could be living in that sand. and make it safe and will it kill the eggs and larva under sand and keep them from laying there eggs? I herd that this makes watering a beech tho is there away I could finish this grow with out having to get new soil medium?