Ammonia Level Troubles

Hello friends!!
I've had my little dude for about 5 or 6 weeks now. Tank was uncycled, which I quickly found out was unwise, but I did daily partial water changes to try and compensate. All was well until about 2 weeks go, when I realized he had been lethargic for a day or so... Tested my water (using API's ammonia test kit) and found the ammonia to be really high. When I took his hide/cave out, I realized that it had been hiding a lot of poop and food... I'd been moving it around when I cleaned, but had never actually taken it out (it was a hollow plastic thing probably not meant for aquariums and I think poop was somehow getting actually inside it... he now has a PVC pipe hide). Eventually, at the advice of the breeder I got him from, took him out, did a full water change, let the filter run for three days, and retested. As a precautionary measure, I also decided (about a week ago) to buy Seachem's Stability. I know artificial cycle starters aren't ideal, but I don't have many other options. Around this time, I also broke the glass test tube that comes with the API test kit. At the time I started the Stability, the tank ammonia was at about 0.25. In the two weeks since the aquarium disaster, he's been eating normally and shown no signs of stress. HOWEVER I just tested and it's at a 0.25-0.5?? I'm currently doing about a 25% water change but is it possible that plastic test tubes vs glass change the reading?? I clean daily with a turkey baster and feed 2-3 times a week.

This post was super long and I'm sorry so here's a summary:
-1 adult axolotl in a 10 gallon tank with a sponge filter, no substrate, some plastic aquarium plants and a PVC pipe hide. Temperature is kept between 60-70F with frozen water bottles and ice packs changed a couple times a day
-Acting normal with no physical signs of stress
-Just finished a week of Seachem Stability
-Can plastic test tubes affect ammonia readings?

Thanks in advance!!

Do you have a liquid test kit for nitrite, nitrate and PH as well as ammonia? You will need to test for these daily whilst your tank cycles. Here is a link on cycling. Have a read through as it is important to understand the processand how it affects aquatic life.

Scales Tails Wings and Things, What is Aquarium Cycling? How to Cycle your Tank

You will need to keep doing daily water changes whilst the tank cycles. A cycled tank will have zero ammonia and nitrite and a reading of nitrate (but you should keep nitrate below 40ppm). If you keep your axolotl in the tank whilst establishing the cycle, you will need to keep ammonia and nitrite down to 0.25ppm. Personally I don't like the use of the bottled bacteria and have seen issues in the past of a 'false cycle'. I cannot 100% determine that the bottled bacteria was the cause but I am fairly suspicious of it and have had no issues cycling tanks without it. But it is up to you whether you use it.