free vs total ammonia

[hubes1]

I purchased the Seachem test kit and just added some live rock to my system. I'm having trouble figuring out which one I care about in terms of determining whether my cycle is progressing and when I can add livestock.

I haven't been able to get a RO/DI unit, so I used tap water + AmQuel. I assume total ammonia measures the ammonia that the AmQuel neutralized?

Last night, I was measuring:
Free ammonia - 0.02
Total ammonia - 6 (off the scale)

Trying to determine whether I need to do a water change to keep my rock happy and what to monitor going forward.

Thanks!!!

[Randy Holmes-Farley]

No. I do not know whether any kits measure the form of ammonia after it is bound by Amquel, but when kits talk about free vs total ammonia, they are talking about something different.

Ammonia, NH3 or free ammonia, is is very fast equilibrium between NH3 and ammonium, NH4+. Total ammonia is NH3 + NH4+:

NH3 + H+ <----> NH4+

The higher the pH, the more is in the NH3 form. If that kit is correct, then the pH is low. However, I wouldn't assume that it is correct.

The NH3 form easily crosses membranes and enters cells. The NH4+ form cannot cross cell membranes as easily, and so does not cause as large of a problem for fish and other organism.

As to cycling, it makes no difference which one your track. Before adding fish, it is best to have zero of either form.
Personally, I'd just focus on total ammonia.

A water change might be useful.

[hubes1]

Thanks for the help! I'll try do a water change tomorrow.

My pH level is ~8.2, so it seems like it's in the correct range.

FWIW, here's the reply I got from Seachem; they suggested focusing on just free ammonia since it's the toxic form, but it'll probably be safest to have them both 0. I'm actually going to top off my water level today and I'll measure my tap water + Amquel to see what its ammonia readings are.

"Total ammonia is a very general measure that is used by most test kits. Free ammonia is the gas state of ammonia in water. In other words, ammonia as a dissolved gas in water. This is the really toxic form of ammonia. At higher pH most of the ammonia is converted to free ammonia and so, being more toxic, this is the form that is most important for which to have a reading. It is also the easier to test for in our test kit. Simply place the sensor in the test sample water and let it sit. This will read the free ammonia. [snipped some upselling of other products]"

[Randy Holmes-Farley]

It is also the easier to test for in our test kit.

Perhaps reading into that is that the total ammonia measure is not very accurate via that kit.

For most purposes, it makes no difference which one you monitor as you do not want any of either, and the exact relationship is determined precisely by the pH and no other variable (in a reef aquarum).