Does this occur after an irrigation? Use more perlite in your soil. in something with high water capacity liek soil or sphagnum peat, you want 50% perlite or similar drainage amendment. Its virtualyl impossibly to overwater if you stick to this.
you need to saturate entire substrate, so don't stop doing that as the ramifications can be far, far worse if you do stop. wait for top 1" to dry, maybe even a bit deaper if it seems like the pot has a lot of weight to it before re-irrigating. The weight of the pot is a better thing to become familiar with when choosing timing of irrigations.
If light were causing this, you'd see very tight internodes (distance betwen 2 growth nodes). As long as those are properly spaced -- not bunched up or too stretchy -- the light is fine.
guesstimate DLI from your light's specs. This can also help confirm light is not the issue here. if DLI is around 35-40 or less with ambient co2 conditions, then it's probably fine. elevated co2 can go as high as 50-60 DLI.