Hi all,
I should say straight away that I wouldn't ever add ammonia to a planted tank, <
http://www.ukaps.org/forum/threads/should-i-fishless-cycle-a-new-planted-tank.27103/> and I've never kept a non-planted one.
I just thought should go back to 0ppm form 5 in 24 hours
Ammonia (NH3) is pretty toxic, but unless you added enough of it to kill all your plants and your filter bacteria, you can be fairly confident that you didn't still have 5ppm ammonia. Plant/microbe systems are very effective at biological filtration, and the large surface area of your tank would ensure that oxygen isn't a limiting factor.
The real problem is that testing for ammonia isn't as straight-forward as many forums would have you believe. Because it occurs as both a dissolved gas (NH3) and an ion (NH4+), dependent upon pH, most test kits measure "total ammonia nitrogen" TAN as NH3. It should say on your test kit whether it is a "Salicylate" or "Nessler" test.
There a number of problems with this, and the measured values may have little to do with the actual ammonia levels. If the test gives a green/blue colour? it is a salicylate based test ("
free ammonia reacts with hypochlorite to form monochloramine. Monochloramine reacts with salicylate, in the presence of sodium nitro-ferricyanide, to form 5-aminosalicylate"). The efficiency of these tests declines over time as chlorine is released from the sodium hypochlorite reagent.
Nessler reagent tests also have some problems, but are more stable, my suspicion would be that they aren't still sold due to the mercury issue? if it is a Nessler test it will give an orange colour.
We do some ammonia testing (as NH4+ with an ion selective electrode), but even then values are open to question due to interference by sodium (Na+) etc. Why use an ion selective electrode? because it gives you a more consistent result than the tests do. Would I make decisions based upon it? No, because it is still not reliable or repeatable.
cheers Darrel