Don't worry about discoloration, this is to be expected with organic nutes. Pay close attention to your roots, check them every day. If the roots are hairy and don't smell, and still have color, you're laughing. If they develop a slimey material and start to smell, you're in trouble.
I woudn't use Piranha for the sake of increased yields or root growth. In my experience, Piranha is best served as an attack nutrient if you already have problems. Sensizym is a much better (in my opinion) maintenance product, with piranha as an attack suppliment. Save yourself some coin, and put the Piranha on the shelf for later, and hope you never need it!
I don't have any experience with tarantula, so I can't comment on that product.
If your dead set on using organics with hydro, then you need to start using a tea method for your powder nutes. Don't mix the powder directly into your solution, it will never, ever mix completely (trust me, ive sat there ravaging the water with a wisk for 30 mins, and it still settled). Go into your sock drawer, and find a nylon dress sock. Measure your powdered nutes, and drop them into that sock, then tie it off and toss it into your liquid mix. This will prevent it from clogging up your pump and sitting at the bottom of your res, and make your cleanup much easier.
It's not the end of the world if you mix them directly in, they will still do the job, but cleanup is just a mess, and you can mess up your water pump by driving sandy material through it.
My last word advice that I have, based on my trials and errors, is skip the organics in hydro if you can. The only time i've used organics in hydro, was to save a crop from root rot when I didn't have my temperatures dialed in. Hydrogen peroxide, proper temperatures, and a nice clean solution will always get the job done. Hydro is better served to be clean, and efficient with chemical nutes. Try to use AN's chemical line with hydrogen peroxide (35%). Once dialed in, youll get comparable results with incomparable price differences. Save the organic growing for soil, and as a solution to a problem you created by being a boner with your chemical nutes
Best of luck