How much water conditioner?

50

Yeah just follow the directions according to how much new water you're adding.

I wouldn't stress too much about adding the prime before, during, or right after refilling.

50. You only use enough Prime to cover the amount you lost during a waterchange. Read the directions on the back of that bottle for exact dosage.

Dosage for 50 should be fine. Keep in mind, however, that if your tap water is extremely high in chlorine or chloramines, you may need to double or even triple the dosage.

This reply might be a little bit off topic but I'll post it anyways.

I've never used Prime and in my case, don't see a need for it. I simply use a regular dechlorinator/dechloraminator. I also don't follow the direction of one drop per gallon. I just spray it on the plastic tub and let the pump do its magic.

With regards to your question, dosage for 50 gallons should be fine and a bit over it should be fine as well. Now if you douse half of the bottle, it might be a different story.

i always treat for the whole tank when im adding it like that.. it cant really hurt the fish so it just makes for piece of mind..

i use prime because for the price you cant beat it.. calculate the price it costs to dechlorinate a gallon of tapwater using the conditioner vs the price using prime.. you will find that prime is a helluva a lot cheaper

I only treate the new water, prime cost to much to waste. I fill two 20 gallon trash cans with water and put enough prime for 20 gallons in each, then pump them into the sump.