What are the best tips and tricks to lower the temperature in my grow?

Air conditioner. This is the only real option to do anything significant. You can run lights at night. If ambient temps (sans grow op) are cooler at night, the resulting temps in the tent will be cooler, too. Potentially save some money in electricity by operating in off-peak hours too. Evaporative cooler will potentially drop it a degree or 2, but then you also add moisture to the air. If a dehum is running harder this will amount to more heat and be counterproductive. Dehums add a ton of heat to accomplish their task - significantly more than the cooling effect of water evaporating. If a dehum does not turn on due to the evaporative cooler, it still won't do much as they are not that effective to start. If you raise humidity a bit, the plants will be more robust to higher heat. Just don't push too much higher than 60-65%. Obviously that doesn't help much if it is already near this range. I'd stop spraying the walls. Increasing risk of mold growth exponentially - much more concerning than 30c. Also, take note of how far the temps drop when lights go out. This can cause a big spike in RH% and if dewpoint is hit, you will eventually grow mold on the plants. This has the greatest risk when the plants are fully grown. Higher temps mean a lot more absolute humidity (not RH), which increases dewpoint significantly. 30C and 60% RH is 21.4C (70.5F) dewppont, which is quite easy to hit after lights out. Anything but a large 600-900 watt dehum will be able to prevent it. Downsize your grow - use less watts for lights and you generate less heat. Sometimes you just want something that is impossible. I had to downsize due to RH/dewpoint issues outlined above a few years ago and that was growing in an ambient 30-35% RH in winter months. If the lights are total trash, more expensive high efficacy lights might help reduce how much heat is added. Small differences in efficacy wouldn't be worth the cost. open doors to impact where heat flows in your house, change house thermostat... just common sense stuff you can use to manipulate it slightly. e.g. if i keep doors closed upstairs around thermostat, i get a few more degrees of warmth down where i grow. If i opent he doors, i get a few degrees cooler (F, this time, was in C before, "1-2 C" differences). outside of an air conitioning unit, there's very little you can do.