Mostly the only real difference between coco specific nutes and general nutes is that they contain more calcium and magnesium. Any general nutrient line will work, but you will need to add a separate calmag bottle to the mix.
I used GH 3-part for years, but any line works as long as you stick to their NER (nutrient element ratio) and dial in the correct EC for the crop you're growing (e.g., tomatoes take higher EC than cannabis so a general line will have the strength levels much higher because they figure most people are growing tomatoes, eggplant than cannabis).
GH should be mixed in these ratios:
1/1/1 micro/gro/bloom for seedling and early veg
2/3/1 micro/gro/bloom for mid/late veg
2/1/3 micro/gro/bloom for flower
Silica is very good to use, but you can skip it your first run. If you do use, say Armor Si, then you would add it to the water first and let it bond for at least an hour.
After an hour or so (or overnight), add calmag, and then the 3-part using the above ratios according to whichever growth stage you're in. Keep in mind those are ratios and not ml's. 5ml/2.5ml/10ml and 1ml/0.5ml/2ml are both a ratio of 2/1/3 but are vastly different EC levels.
It's also not a bad idea to use a microbial, like GH's Defguard. You can save money and use Southern Ag Fungicide (I haven't personally used this). Either way, they both are bacillus amyloliquefaciens to a concentration of 98.85%. This is far better than Hydroguard, which a lot of people use due to the Botanicare name, which is the same thing but diluted down to 0.038% and costs around the same per pint as Defguard but you obviously have to use a lot less when it's 99% concentrated and get more for your buck.
Running a microbial can help prevent root rot. Some people use H2O2 or pool shock, but running sterile can be challenging due to the nature of plants. Pick one or the other. You don't want to use both a microbial and a sterilizer.
EC levels (can depend on strain):
0.4-0.5 for the first week (some people don't feed nutes at all until day 5-7, but I hit it with nutes 24 hours after it's popped up from the coco and get great 1st week growth)
After a week of ~0.4 you can start hitting it with about 1.1-1.3 for rest of veg.
Flower, 1.2-1.6. I usually don't go much above 1.2 anywhere during the grow.
pH is acceptable anywhere between 5.5-6.5, but certain nutrients are more available at the higher range and others more available at the lower range. That being the case, you want to be in the higher range the first week, like 6.2-6.4, and then work it down to around 5.8-6.0 by week three and you can pretty much stick to it there for the rest of the grow. Again, it's not going to shit the bed if you just went 5.8 or 6.1 from start to finish, it's just that it's most optimal to be in the higher range during seedling and the first week of veg due to calcium.
