Probably not.
What is on the label is only what is promised to be in there. There will be an unavoidable bit more you just cannot plan on. Also, the amount of ml you use make a huge difference at a concentration of 8-8-8. Figure that is 4x more concentrated than a 2-2-2. Every little bit you over do it will be a larger issue.
You can do a little math to figure out an approximate EC for the solution if you don't have a meter. Nutrient values are in parts per hundred, so it's just a matter of converting to ppm and then compensating for your solution volume.
For Nitrogen you could take the percentage on the label and multiply that by 10,000 to get the ~ppm in the bottle of N. Then you divide the number of ml of water (a gallon is 3780) by the ml you used (like 10ml). Divide the first number by the second number and that gives you an approximate N value (within 20%).
On the label P and K are listed as P2O4 and K2O so you need to understand that the actual level of phosphorus is only 44% of what is listed, and potassium is only 83% of what is listed.
An 8-8-8 at 10ml per gallon would be:
(8*10,000)=80,000
(3790/10)= 379
(80,000/379)= 211ppm N
(211*0.44)= 93ppm P
(211*0.83)= 175ppm K
You then need to do the same formula for Calcium and Magnesium.
211ppm-211ppm-211ppm plus let's say 150ppm Ca and 50ppm Mg
You get about 835. Double that, and you get the standard American conversion for ppm to uS/cm (detailed EC), and it is 1670. An EC of about 1.7 predicted.
Add in the tap water, and compensate for "extra" and your true EC could easily be over 2.0 with a mixture like that.
Get yourself a meter, do a little math, figure out some good ratios and keep you EC under 1.8 for sure and you should have good results. In soil you should be aiming around 1.0 to 1.2 during your stronger feedings which are sporadic at best.
