The plant is assimilating a lot of nutrients from the water. Each time I irrigate I leave all the plants in the cupboard with a similar TDS, and every week, the Kali AK is the one that has absorbed the most nutrients, showing a PPM level that is much lower than its companions. The buds are forming very well, picking up quite a lot of volume and density. I'm sure it will produce great rocks. I am very happy with your development during these last weeks. I hope you continue in the same way.
This week I have raised the dose of Mega Bud quite a lot and I have stabilized the PH, which had been decreasing during the last weeks due to the increase in fertilization. The pH is again at 5.9 and with a water temperature of 18ºC I think the plant has a perfect environment for the assimilation of nutrients.
I have also put the ballast in superlight mode. I hope we can see the result of all the actions this week during the next one since I think they will bless the plant a lot.
About the temp. i recommend you to use what I used on my shrooms : Peltier.
You may buy a cheap water pump of 1/8 and plug to a Aluminum block and make the water circulate within the buckets. At the aluminum you put the Peltier (with a good thermal paste that's essential) and fix very tight, and at the hot side of peltier a good and large PC heatsink with a good cooler.
The Peltier makes the block cold, the water pass within and goes to the bucket making it cold. The peltier has two side, the chill and the hot, at the hot you must dissipate the heat otherwise it wont chill. SO... Chill it outside from your tent.
You must note that the pump shouldn't be much higher than the bucket. A 1/8 cheap pump could only lift the water around 1.5m, and that makes it loses the power of circulate water.
So:
Peltier (around 9 amperes would be enough for each tank)
Heatsink with cooler
Water pump 1/8
Aluminum block
12v power supply
And if it get too cold get an "W1209" and put the thermostat inside the water so it will turn off the peltier (if you install that way) when reach the temperature that you desire.
Colder water is best for the roots.
Good luck, any help just ask.