I've been using Advanced Nutrients pH perfect and it's worked well. pH perfect is a bit of a misnomer: you still need to adjust the pH a bit for optimal results. Although I bought pH Down (Phosphoric Acid 85%) and pH Up, I've only ever used the pH Down. My tap water is at a steady 7.0 (lucky me). So, a few drops of pH Down are all that are needed to get the pH in the proper range. If I overshoot, I simply dilute my container with tap water so the pH goes back up and add a bit more nutrients.
A few companies sell coco-specific nutrients. This goes without saying, but with nutes less is more. The only deficiency I've had was Calcium. Other than that, I've had nutrient burn more than once. I've adopted a new strategy of using as little nutes as possible, almost waiting for the plant to tell me it has a deficiency before adding nutrients. Unlike soil, you can change the nutrient conditions very quickly with coco coir. Since it's so porous and drains well, you can quickly add nutes or pure water to adjust any issues with the plant. With soil, you have to contend with whats in the soil already, which can often work against you. The downside is that you have to watch the plants like a hawk, since nutrient deficiencies or nutrient burn can happen very quickly.
Coco coir is essentially made from coconut husks. It's a fibrous material that has excellent drainage, a soilless medium that has grown in popularity in the last years. In this guide I will walk you through my coco plant growing process.
I use 5 parts coco coir and 1 part off-the-shelf perlite. I mix these thoroughly, until the mixture is as homogenous as possible. I next fill my pot(s) with the coco mix. Before thinking of planting, I flush the coco thoroughly with water at a pH of around 6.0. Coco works similarly to hydroponics. The coco itself has no nutrients, so it relies solely on what you put in. This a huge pro and also a con. It gives you ultimate control of nutrient intake. pH should be kept between 5.5 and 6.5, although I never stray outside of 5.8 to 6.2. Invest in a good pH meter. Important tip: use Calmag! Coco coir tends to absorb and prevent the distribution of calcium. The solution is to add CalMag when adding nutrients, per the instructions (it's about 1ml / liter of water).
I also invested in an TDS gauge. This measures the level of dissolved salts: nutrients and naturally occurring minerals in the water. The measurement is in ppm (Parts per Million). This gauge can help prevent nutrient burn by ensuring that the water you put in doesn't have too much nutrients. It's easy to use, and there are several guides online on what your ppm should be during various stages of growth (seedling, vegetative, flowering). I use the gauge to measure the water going in and the runoff out the bottom of the pot. If the ppm is too high I simply dilute the water+nutrient solution, recheck the ppm and pH, adjusting if needed.
It's pretty much impossible to over-water coco coir. If you add too much water it simply drains out of the bottom. You should aim to water the plant until you first see run-off, then add about 20% more water / water-nutrient mix. It should be flushed regularly as salts (aka the some of the nutrients you put in) will accumulate on the coco fibers.
Water when the pot gets "light" in weight. I've learned to pick up the pot and feel when it needs to be watered. You might not be able to over water coco coir, but you can certainly water it too often. This can result in fungus gnats (minor nuissance), or other issues. I generally wait until the pot has lost 3/4 of its weight before watering. A full grown plant needs to be watered every 2 days. A smaller plant in a big pot may only need water every 7 days. Depending on you schedule, you'll likely be watering as follows: (Water with Nutrients, pure water, pure water, repeat). If you have deficiencies you can alter this schedule: nutes-water-nutes-water, or nutes-nutes-water.