According to the chart, 75-80% humidity. As someone pointed out it’s a guideline. Different strains have different preferences. Your chances of developing mould are higher.
Me personally I would keep at 65% max for my grow in veg, 55% max for my flower room and around 75% for my clones and seedlings.
I don’t grow with Rockwool, or use flood and drain. So I couldn’t say for sure if that humidity will cause mould, it would certainly be higher chances of it it developing. I would definitely be worried about powdery mildew though.
I grow in no till organic soil, I don’t have high temps, and high humidity, unless something goes wrong.
With a lower humidity my plants grow faster as they uptake more water and nutrients when experating, but with flood and drain and bottle nutes, you have a higher risk of burning your plants quickly, growing that way.
The only way to know for sure is start growing and work out the kinks, as you go. Which is why people don’t jump straight into a grow with CO2 as it’s more complicated and expensive.
When you have been growing a while you may realize you don’t need CO2, to get great results, taking extra chances of screwing up your grow with high heat and humidity.
There is no cheap ways of doing it, I am about as cheap and redneck as it gets in a grow, I build lots of stuff to save money, and experiment, but you reach a point, where you can’t do that, and CO2 is one of them. The right monitoring, and delivery system is very expensive. I have tried other methods, converting a mason jar into a tiki lamp burner, running on methanol, and at half a litre in 12 hours is not cost effective to extra production. As well as a fire hazard.
My flower room is semi sealed it could operate without the extra CO2 from my wine making, I know because I have tried it both ways, and see little difference.
I don’t allow my heat and humidity to get above the norms now because I have air-conditioning. My CO2 from wine making, is a by product and costs nothing to use. To do it properly will cost a lot of money.
The only way I can see, if you go this route is either getting bigger or more de humidifiers, for each room, or what I have done, use air-conditioning as it gives me better control of both heat and humidity problems in my grow.
Also do more research into it before comitting to it.