Small volume of soil, larger plant... it may be reaching it's limit on that container and local variables. 8-10oz of substrate isn't much.
This plant is old enough you shoudl be fertilizing every irrigation somewhere near 1.3-1.5EC with well-balanced mix in coco+perlite. You want a religious 10% runoff. Wait for top layer to change color and repeat (as coco dries it changes colors). you can pre-empt that a bit, but it's better early on to make sure those roots drive down, not up. it pays dividends later on and later you can increase frequency of fertigation to drive better bud development with a hefty, robust root system.
If you do this you absolutely cannot over or under water the plant... won't happen.. if it does it means someting else is at fault.. drainage quality -- 30% perlite with coco. 50% perlite with soil or sphagnum peat moss -- this is directly proportion to their water carrying capacity per volume... i.e. soil/sphagnum peat moss holds 150% of what coco can. In the end a 70/30 coco pot will hold as much water as a 50/50 spahgnum peat moss pot (with same volume of substrate, of course)
Feeling teh weight of teh pot will be the best indicator if you want to be precise with how much fertilized water you mix up... if you fertigate at same loss of weight / same light feeling of pot, it'll require teh same volume of water each time -- this is what you want to use to determine how much it needs.
With soilless, you always fertilzie because the plant is 100% dependent on nutes from the fertigation - nothig in coco, or shouldn't be. the 10% runoff waste (down drain, outside, but never let it sit in it's own swill) will guarantee whatever concentration you are feeding does not spike. Any symptoms are 100% about ratio of what you feed in this context, which eliminates a lot of confusion when trying to diagnose a problem.
8-8-15 ratio -- not concentration -- is a good place to start in soilless. Ca >100 / Mg >80 / S >100 are ballpark ideas... your tap water and local variables will make this vary a bit, but if you use these ratios / ppms at the npk ratio of 8-8-15 it'll be in teh 1.3-1.5EC range... somem adjustments will be necessary. You may need less N in bloom, for example. Always read plant and react. Take some notes and before long soilless is boring AF and very procedural and very consistent results. All good things.
You've been given some odd advice on watering too. Water entire substrate, never just water the top few inches or with some minimal volume of water that leaves dry pockets in aftermath. Seedlings are a slightly different context, but you still don't want a superficial irrigation. If you get it fully wet before sowing (letting it drip dry 15-30minsn before sowing is fine or even an extra day, but you'll have to wter it sooner the longer that period is), a solo cup should retain that moisture for 3-4 days in most contexts. you'll want to re-moisturize before top layer starts to dry (seedlings / non-sprouted only, not mature plants).
This is only because the little sprout may not have a long enough root to reach what remains moist longer deeper in the cup... definitely can't let a seedling dry out. only use water for this stage, but you can fertigate after they break ground and avoid gettingn any drips on the very senstive little plants. nute water on a growth tip can be a bad thing at this early stage. By the next irrigation you don't have to be this concerned.. stick to the top layer starting to dry before fertigating with 10% runoff or more.
by letting the substrate dry quite a bit, it avoids risks and promotes more robust root growth... it seraches harder for water. For optimal growth rates, at least temporarily, you gas it by fertigating a bit earler... stick to the safe-way early... if you want to dabble in more frequent irrigations, i'd wait for 4-5 weeks or when you flip to flower... then if it drinks at least 25-33% of the weight, you can re-fertigate at that point fairly safely. (overly wet substrate for long periods of time is an increased risk of problems, fyi.. but many ppl do it with no problems as long as the plant is appropriately sized for pot and the pot has excellent drainage qualities.
i do the safe way until flip... then after that my plants can easily handle daily irrigations of 2.3rds gallon or more (40-day vege this time and in "5gal" nursery pots with actual 3.6 gallon volume, 50/50 peat or 70/30 coco is same thing mathematically and through experience). Some people do 2-3 fertigations per day... this is basicalyl matching hydro growth if you dial that in... in my case, i'd probably need slightly smaller pots to do that. Plant's rate of drinking up what is there is key. Need some minimum drinking or all you are doing is creating a puddle frequently :P