Well, it is not rocket science :lol:
Cat urine is fairly high in ammonia and kitty litter can only remove that ammonia which has been converted to ionized ammonia, NH4+. As NH3 gas, it will rise an travels in the room, gets picked up by air pumps and skimmer inlets and settles out on top of the water. NONE of you have NEVER been a house before with a cat and smelled ammonia ??? It is no different that high room air CO2 lowering your pH. And the dirtier the cat box the worse it is. It is not just an issue in reef tanks but also FW or uncovered RO/DI containers. You NEVER place a tank or water holding container near a cat box. Many have had this issue and some have tested the water for ammonia with cat box near by removed it and tested again with no ammonia. An I use to have cat and had the same issues and that was 2 decades ago. There are quite a few post on boards about it, to include RC
From Nanoreefs:
The approximate distance from the cat box to the tank is about 9 feet, and around a wall.
The ammonia test readings performed in triplicate from the Picotank were in all in excess of 8.0 mg/L.
At about day four I placed a small glass of RO/DI water in a clean drinking glass and placed it on the sink counter for one day. Initial reading for ammonia was zero.
After one day of being exposed to the air in the bathroom with the litter box, I tested the water in the drinking glass. Final reading for ammonia was between 2.0 and 4.0 mg/L!
Just to be sure the test kit wasn't corrupted, I used the same test kit in the same vial (after a rinse) with fresh RO/DI water taken from the same source as the water in the glass. Reading was back to zero.
I would say that gaseous ammonia can dissolve very easily into open tank aquarium water. Very rapidly too. The smell from my litter box was not overpowering, but noticeable. I would recommend anyone who may have a cat litter box in proximity to their aquarium use caution and run a similar test. Especially if you have a protein skimmer air intake nearby.
From Aquaria Central:
Your tank isn't near a cat litter pan is it? i know when trying to cycle one of my tanks i ended up with 8.0 ppm ammonia spontaniously because my ait pump was in the stand and the cat box was only a couple feet away. Ammonia gass dissolves in water very rapidly.
From RC:
IMO all those hang on all the hang on tank constant moniters don't work. I put one in my freshwater tank for PH and Ammonia and the\ said nothing for about a month and the Ph kept reading way too low, despite my Ph test. I decided to test the water and I had a huge amount of ammonia and my PH was still above what it said. i changed both the cartridges and they continued to read incorrectly a few days later, and changed again with similar results. Also, Never, EVER put a fish tank next to a cat box with little room circulation. You will have sky high nitrates and huge ammonia problems. It is what killed my freshwater aquarium. Just my experiencs though.