Hydroponics solution is what should be used even with soil plants. The reason being it basically has everything a plant needs to live in it since water alone does not have these attributes. There are 14 nutrients that a plant needs to survive. But the 3 main nutrients that come to mind are Nitrogen, Phosphorus and potassium.
During grow cycle the plant likes a fertilizer high in nitrogen. Something like 20-5-5. It uses the nitrogen for strong stem and leaf growth. After you change over to your flowering cycle you will want a fertilizer that is high in phosphorous and potassium. Something like 5-15-15 should work well.
PPM or parts per million is the measure of salts in an amount of fertilizer that is in a water solution. You will need a PPM meter to read this.
Try to keep the seedlings and clones at about 100-250 ppms. After about 10 days bump up the ppm to around 500-600 ppm for the next 2-3 weeks. After about a month raise it to 800-1000 ppm. When it starts to bud it should be at around 1000 and start taking it up slowly to no more than 1500 ppm.
If you over fertilize your leaves will start to burn. If you see this you will need to flush immediately. Just use pure water and basically drown the plant. Four times the amount of grow medium should be fine. If you use tap water it usually has a ppm of 250 in that area. All you need to add 250 to whatever your shooting for. So for a 1000 ppm the meter will read 1250.
After the hairs on the buds get 1/4 red I stop feeding the plant nutrients and just give them pure water. This will allow the plant to use up the nutrients it already has and makes the smoke taste a lot smoother with out all the chemical taste.
So controlling the PH in out nutrient solution is very important for healthy plant growth and good nutrient absorption. Marijuana thrives in a slightly acidic medium. For soil plants, aim around 6.2-6.8 for hydroponics look to be around 5.5-6.5. Best way to figure out your PH levels is to buy a ph meter.