New to led / normally grow under 1kHPS

You don't need co2 at night, but may want it on slgihtly before lights turn on to reach that 1200-1300 range by the time the lights do turn on. if you don't have light stress or very tight node spacing under 55DLI, then all is well in that regard. VPD impacts how many grams of fertilizer enter the plant per day (transpiration is primary driver behind rate of drinking). If that changes, you may need slight adjustments to EC of fertilizer. The EC you need will heavily depend on local variables. Also, is that including tap ppm? If so, it's probably in a normal range anyway. But, with more light and more co2, it can use more building blocks that fertilizers provide, so you'd need more of them than someone with ambient CO2 and 35-40 DLI... in addition to VPD having its impact too. based on growth it need X grams of each nute and if rate of drinking changes, that doesn't change those needs. So faster drinking (higher vpd) will need a slightly lower EC and vice versa. It's something you can use to pre-emptively avoid a nute-issue if your VPD does swing - intentionally or not. Don't worry about the runoff being different. Is it consistently different? that is the key. The runoff is not very reperesentative of what is in the substrate. If you have a religious runoff at least 1/day of the 3 irrigations, it should maintain a consistent level of nutes. Any issues seen will only required adjustment to formula to fix. no worries about buildup or leaching of the substrate if your fertigation habits are proper in a soilless context. One thing i'd change is that there no perlite or similar in that coco? Use 33% in coco (the pre-packed 70/30 being good enough too). This may require some adjustments on your part as far as a proper plants size to pot size ratio to effectively do 3x/day fertigation. The pot will hold a little less a water per volume, but you'll get a more optimal mix of gas:water in the substrate which is better for root growth -- more effectively make use of all that extra carbon and extra umol/s PAR. I'd suggest vermiculite, like bugbee. It releases some plant usable silicon, unlike perlite or pumice stone etc.