I think Is a K deficit !???

first off before you go change a bunch of stuff check your run off PPM if its above 1000 you can start hurting your plants. Yes some plants can take more but its a fine balance between over nuiting and finding their peak nuit intake.

Hello Aliescrog, from what i can tell from your information. U are in flower and your lightschedule is 18 hours of light, where it should be 12. Your temprature is 27 degrees and at this stage in flower it should bebetween 23.5 and 23.8 during the day and 17.5 during the night. Both day and night are too hot from what i can tell from your infromation. So to mee it doesnt look like overwatering but more like heatstress in every way possible. If you correct that i think everthing will bounce back to normal. I hope this answer was helpfull, Keep on growing brother. Peace 👍

Always get your watering and ph right before looking at a nutrient issue. I’m also using biobizz, which is ph neutral. But the good microbes in the soil can raise ph with their waste. Both overwatering and ph issues can lock the nutrients out. If you compensate by adding more nutrients you can end up stressing them more and making the situation worse instead of better. In a week of flushing with water adjusted to ph 6 I shifted the soil ph from 8 down to 6.5.

Too much water. Roots are stressing due to heat or cold and it cant absorb proper nutes now so it's a little deficient. Wait till soil completely drys then just continue with half nutes and dry again then add full nutes . Then u should be good .

Your plants are showing signs of underwatering/overwatering. U need to fix this problem. Sometimes a cannabis potassium deficiency (like all deficiencies) can be triggered by stressful conditions (for example overwatering, heat, transplant, etc) and may clear up on its own after the period of stress is over. If you only see one or two affected leaves near the bottom of the plant, and the problem isn’t spreading, I wouldn’t worry too much about it! When you water next time left pot each day to get a feel for weight and when it's light time to water. I don't check with fingers cuz all the water sits at the bottom. So if you are watering when top layer is dry more than likely your overwatering.