Ohh and I'm tempted to help with the calculating part so here goes (the warning is I'm a chemist so I do it the long way - just ignore it if you're bored out of your mind and skip to the very last part)
Here is what is called the dilution formula (essentially you are taking a concentrated solution (your 10% ammonia) and diluting in your tank to obtain a dilute solution):
CconcentratedxVconcentrated=CdilutexVdilute
Where C stands for concentration and V for volume. The concentrated will be your bottle of 10% ammonia and the dilute will be your tank.
You want to know how much volume of concentrated solution to add so solve for that (I'll abbreviate the names somewhat):
Vconc = (Cdil x Vdil)/Cconc
The important part it to keep Cconc and Cdil on the same units, in this case ppm, and whatever units you use for Vdil is what Vconc will come out as. You won't need to use gallons on concentrated stuff only mL so we will need to convert the volume of your tank to mL.
Plugging in the numbers:
Cdil:
This one is the easy one, it's whatever you want your ammonia at, but this assumes no ammonia to start with so if your ammonia is 0ppm (you might see this happen towards the end your cycle) then its 4ppm but if it's say 0.5 then you want to add enough the get to 4ppm so it's 3.5ppm. Whatever the difference between between what your ammonia is at and the level you want it at - that is your Cdil
Vdil:
Like I said we want mL here.
Your tank is 29gal and you can assume that 10% of that volume is taken up by decor and substrate so let's go with 26.1gal.
Multiply by 3785 to go to mL (don't have a calc right now and I'm too lazy to close the app and use my phone).
The hard one:
Cconc:
We need this in ppm so we need to go from 10% (I'll assume it's weight to volume which what these usually are, the other thing it could be is volume to volume but I doubt it, I can explain why if you want so let me know if you're curious - but I did this when I cycled my tank and it worked fine) to ppm (parts per million).
Part per million can be thought as for example 1ppm as 1g of substance (ammonia in this case) for every 1million grams of solute (water in this case).
So back to the 10% we are assuming weight to volume so 10g of ammonia for every 100mL of solution. This is a dilute solution so we can use the density of water to go from volume (the 100mL) to mass (we want grams). The density of water is 1g/mL so 100mL is 100g. So now we have that the conc solution is 10gammonia/100gsolution we need parts per millions so the 100g should be 1million g. So we need to multiply top and bottom by 10,000. That gives us 100,000g ammonia per million that is 100000ppm
Cconc = 100000ppm
So for your tank:
Vconc = (Cdil x (26.1x3785)mL)/100000ppm
Cdil = 4ppm - ammonia level your tank is currently at.
Hope this helps
