in regards to the tin shed maybe try installing a couple louvers on it to let some airflow in the air, the humidity can be fixed with a humidifier and if you got the money you could even try an air con to cool the shed. I'm doing my first dwc grow with just normal tap water and coincidentaly sensi ph perfect nutes myself and at first I was skeptical but the shit works. I dont say it works in that you'll get miracle growth compared to other nutrients same growth rate but the nutrients don't nessairily stay at a perfect ph range it's that they are available at a much larger range so ph fluctuaion is okay but for the most part it finds it's "sweet spot" for the first bit i checked the ph and all that but i'm 4 weeks in flower now and I haven't had ANY nute toxictiy or deficiencies. I say fuck
advanced nutrients in the sense of buying 10 different additives and all that but their ph perfect line does work as stated.