Hope it was easy to follow. Sometimes I restate simple things because experts like the confirmation that they know all the beginners stuff, students benefit from repetition and smart people enjoy learning something new.
My advice for next time would be to drop the K2SO4( KNO3 adds enough K) and mix 30x the weight of KNO3, KH2PO4 stated in my first post. Than the bottle will last 30 times more. Check the solubility of the 2 first.
You can make the switch at any time really. People do both, from my point of view for small aquariums it is impossible to obtain a degree of accuracy when dosing solids and I do not like my fish to nibble on the granules. It helps that dosing pumps work with liquids
Yeah, so pet-peeve of mine... while I understand why Tom Barr and Co. did this, I do not agree with them endorsing it. The rationale is simple, since we are working under the philosophy of "add more than enough"... you do not have to be exact; since it is for everybody, this is a way for everybody to do it. Does it mean you should do it ? Your choice, below my counter argument ( may sound sometimes smug to some people)
Since we want to obtain a target concentration of mg/L in the aquarium, it makes sense that we would measure the weight of desired fertilizer.
TEASPOONS ARE NOT MEASURES OF WEIGHT. There, I said it. They are at best used to measure volume of liquids. Try this, take 5 teaspoons of a salt and weight them on a precise scale, calculate mg/teaspoon. Take 10, take 50, take 5 again, ask your friend to do the same... chances are that every time you get different amounts.
Add to this that we are dealing with salts, which have various sized crystals depending on the manufacturer standards, industry grade will be coarse, lab grade will be fine. How do you think this affects the density of the salts... and thus the weight of salt in your Volume measuring tool, the teaspoon. According to my own observations and that reported by other members online you can easily introduce a 2xtarget amount error and between users it can vary by as much as 5x. And then you see people on the forum saying that they use EI and have N deficiency or have 80+ppm NO3...might this be one factor ?
For most people on this site I do not find it too much of a trouble to use a scale. If you need to dose too little to accurately weight make a solution. Just my rationale.