Alright, I find in these times it's best to look at what we know, what we are doing, what we see, and the results we are expecting. It helps keep the information more organized, and if anyone has a solution it makes the thread much easier to follow.
Your parameters in the morning have tested as:
Ammonia: .25ppm
Nitrite: 1.0 - 2.0ppm
Nitrates: 5 ppm
Tap water ammonia level was .50ppm higher than the tank's, which means we can assume that your actual tap water's ammonia level is .75ppm
So, we know that the cycle is stalled. You started the cycle as fishless while dosing prime and stability, but you initially received no results. Those results you were looking for were the beginning of the breakdown of ammonia, into nitrites, and nitrates. Then you added 3 Zebra Danios, and noticed the cycle initiated. You have been dosing prime since the start up of the tank. At one point, you thoroughly gravel vacuumed, skipped water changes, and just dosed prime. You performed water changes of either 25% or 50%. Then you made a switch from Seachem Stability as your only dosing source, to Seachem stability and Tetra safe start together. All paremeters are tested with an API test kit.
Lets look at what you're dosing and what they are suppose to do. So I had to re-fresh myself on these products, because it has been a long time since I have been involved with them, and I never trusted them. I got all information from their websites.
Seachem prime is advertised as follows:
"Prime also contains a binder which renders ammonia, nitrite, and non-toxic. It is very important to understand how those two functions work together.
The reduction process also breaks the bonds between chlorine and nitrogen atoms in the chloramine molecule, freeing the chlorine atoms and replacing them with hydrogen to create ammonia."
So from my understanding, it does not actually remove Ammonia but creates it. However, it will render ammonia and nitrite non-toxic, and still usable by the beneficial bacteria. The only thing it eliminates is Chloramine, by reduction, and then replaces the chlorine atoms with hydrogen. I think there is a need to better understand that process, just like they have mentioned.
Seachem Stability is advertised as follows:
"Stability is completely harmless to all aquatic organisms as well as aquatic plants, thus there is no danger of over use.
Stability is the culmination of nearly a decade of research and development and represents the current state of the art in natural biological management.
The bacteria used in competing products are inherently unstable. The conditions necessary for their growth and development fall into a very narrow range of temperatures, pH, organic loads, etc.
When any of these parameters are not strictly within the proper range, the bacterial culture quickly crashes and dies. Stability does not contain any of the aforementioned bacteria."
What I've taken from that for myself, is that there is no benefit from combining Seachem Stability with Tetra Safe Start. I did not feel the need to post anything from Tetra Safe Start, because it was mostly generalized, from what I could find. It seems that depending on your parameters, Stability's bacteria could end up out-competing the Tetra Safe Start's bacteria anyhow. This is all hypothetically speaking, of course.
I have found a consumer's comment about Stability that may be useful for you:
"I've been using this product for a while, it's pretty good stuff but you need to take into consideration that the instructions on the bottle are not going to have your tank cycled in 7 days.
The way to use Stability is along with Seachem Prime water conditioner, and water changes. You want to dose both of these daily while you fish-in cycle your aquarium. The formula that I have been doing is as follows.
If you have less than 1 ppm ammonia or nitrite - dose Stability and Prime, wait 24 hours and check again
If you have more than 1 ppm ammonia or nitrite- do atleast 50% water change, sometimes 75% is best depending on how high your ammonia and nitrite is. Then dose Stability and Prime.
The key to cycling your tank and keeping your fish healthy is to keep ammonia and nitrite below 1 ppm, by using Prime Water Conditioner because it will bind these into non toxic forms for 24 hours. This also allows your growing bed of bacteria to have something to eat on.
I am currently cycling a 20 gallon long tank, with one Oranda Goldfish. They are large waste producers, so I normally double my prime dosage and quadruple my stability dosage just to be on the safe side. Amazon by far has the best price for the 500ml bottles!"
Let's do a general overview of how the nitrogen cycle works. Let's leave out all the particulars for now. Bacteria enter our aquariums naturally because they have different tools. Be it facultative, aerobic, or anaerobic. I will explain things in the Saltwater sense, because the cycles do not differ. Saltwater systems take advantage of a Protein SKimmer, because a certain group of bacteria consume these proteins, and the by-product is ammonia. Then of course that's where your cycle starts. You know how the rest goes. Protein skimmers in aquariums, are only condensed and less complicating versions that your local water treatment plant uses to treat your water! Because it eliminates the first source that promotes the growth of multiple harmful pathogens. Nitrates just end up being used by plants or consumed by another bacteria that convert it to nitrogen gas which naturally leaves the water surface.
I do not believe in these products, though I am sure they work. I do not see how the bacteria survive in these bottles for a very extended period of time. You spend a lot of money, and if you are going to do it, it seems you most follow it precisely. Personally, I recommend setting up a take and buying pure ammonia with no additives from the store. Does that to about 4ppm, and let nature do it's job. The bacteria will enter the system naturally, even if it longer. I can see Prime being useful in an emergency situation. You can actually grow a colony ten times larger than your initial stocking, and they adjust accordingly and naturally.
With that being said, I think you may be possibly doing to much. These bacteria live on surfaces, from my understanding. Not the water column. removing water should not effect them significantly unless the areas they inhibit are completely dried out. I think you need to slow down, and regroup. Get in touch with people who use these products, or research them more. I think your cycle is nearly complete. Given the numbers you have given. Ammonia decreasing, nitrate varying, and more than likely nitrates going past what your test can detect. Nitrates are okay, as long as not to high. Regroup, slow down, and figure out what is going on with your products. I think that's where your problem may be. Because everything else makes sense to me. I could be wrong, I am no scientist but I am enrolled in the Microbiology which helps me further understand these processes.
*Edit: I forgot to mention this as well. It is also out of curiosity and I am hoping that someone has an answer! But if Prime does not eliminate ammonia, but makes it non-toxic, then how does that affect test kits? I'm wondering if it gives you a "false reading," when you are expecting the Ammonia level to be zero in the first place.