Yes, dose for the full 20 not just the 10 you put back in.
If that's your tap.... it shouldn't be.
Wait, what do you mean tap from tap?
Also, what do you mean when you say "cycle length"?
Cycle means the process that takes days and weeks for the ammonia from the fish pee and poo and decayiing food to finally cause the ammonia loving bacteria to flourish and start breaking down the ammonia into nitrite.
Then, the nitrites have to be in the tank a while to encourage and feed the nitrite loving bacteria that must flourish and eat it up and convert it to nitrates. This takes time.
Cycling is not doing water changes. It takes a lot of time, unless you know someone with an established healthy tank that has a boat load of beneficial bacteria and will give you some filter squeezings or a piece of their biofilter to put in your foam/sponge/media portion of your filter. The bacteria-in-a-bottle does not usually have live bacteria because they are sensitive to heat and those products are shipped and stored in less than desirable circumstances.
Your 30 gallon needs an immediate water change to get that ammonia down from 2.0 to as close to .25 or less if you can, but lord, I don't know with your tap water... you're going to have a heck of a time keeping things safe in your tank until you get a boat load of bb yourself.
I'm wondering if your test kit is out of date or otherwise bonkers. I think I'd take a sample of tank water from each tank and go to the lfs and have them test it to see if their findings match yours. You did say they use liquid testing, right. I'd do that for sure to see what they get.
At any rate, once your tanks are cycled and have a healthy colony of the beneficial bacteria they should be able to handle the ammonia from your tap and fish, as long as you don't over feed, and you practice good tank maintenance and do regular water changes with vacuuming of the substrate to keep the gunk and decaying matter from building up. You have to be careful when you vacuum if there is a lot of gunk in the gravel. Too vigorous vacuuming and stirring it up can cause a spike, too.
Vacuum an area in your tank, say one third or one half, when you do a water change and then the other half, or third, on the next water change and so on.
Even if your results are accurate and you are getting those readings from your tap, once your tanks are fully cycled you should have enough beneficial bacteria in your tanks to handle the ammonia that your fish produce in addition to the ammonia in your tap water. You will definitely want to continue to use a conditioner that detoxifies ammonia, and I'm afraid you're going to need to monitor your parameters closely, daily, even after the tanks are cycled, and do water changes as needed to keep the tank healthy.
