What's at the bottom of the tank?

Hi guys, I’m a new member and I know very little about what I’m doing. When I received the little guy, I was told to clean out a quarter of the tank once a week. I have neglected to do that so on Sunday I completely cleaned out the tank (replacing all the water with new de-chlorinated water). I didn’t use any soap or bleach because I’ve gotten the sense online that that was dangerous to the axolotl. I know to use an anti-chlorine solution but I had no concept of cycling. I’ve changed his water out completely before and he’s somehow stayed alive. However, the night after I cleaned it out there was a gray substance all over the bottom of the tank. See the images attached. I can’t imagine he would produce that much waste in that amount of time plus it doesn’t look like his waste at all.

My uneducated theories are these:
1. That the filter is the problem. My dad got a new filter recently (the old one had been broken for a couple weeks) and it is a size larger than it should be for the size of the tank. The tube as you can see in the pictures reaches all the way down to the sand. It was on but not churning water when I arrived.
2. That the sand is the problem I thoroughly cleaned the sand for the first time in ages so perhaps the necessary bacteria didn’t eat up whatever is at the bottom of the tank?

Since the pet stores were closed when I got a look, all I could do was change a quarter of the water out. What I’m doing today is getting him an appropriately sized filter, a new siphon cuz my old one broke, and a testing kit I guess? What is the gray substance though? Any ideas?

Cycling is the most important factor of housing an Axolotl.

Your Axolotls needs to be in a healthy environment, so like humans would die being kept in a room full of toxic gases, Axolotls must be kept in water which does not contain toxic chemicals.

The Nitrogen Cycle is key to giving your Axolotl a safe environment.

You will need a test kit to monitor your nitrogen cycle, because you have to check for levels of Ammonia, Nitrites, and NitrAtes. These are what basically make up the Nitrogen Cycle. A lot of users on this forum use and recommend this test kit including myself: Welcome to API Fishcare: FRESHWATER MASTER TEST KITThis liquid test kits are far more reliable that the test strip versions. You can purchase the above kit from Amazon.

The cycling process can take from 3-6 weeks. For your tank to be cycled, a beneficial bacteria needs to be present to break down the Ammonia and Nitrites into Nitrates. Ammonia and Nitrites are lethal to Axolotl and are produced from your Axolotls waste and decomposing food. Nitrates are a slightly less toxic by product. During cycling the beneficial bacteria will colonize your tanks surfaces such as substrate, ornaments, filter, and begin to feed on the Ammonia turning it into Nitrites, then bacteria will break down the Nitrites into Nitrates. The bacteria is known as a 'biofilter', as it filters the ammonia and nitrites into less harmful nitrates.

Once this cycle is established by the beneficial bacteria colonizing the tank, the Ammonia, and Nitrites will always be filtered by the bacteria into Nitrates, all you have to do is monitor you cycle by testing your water weekly so that when your Nitrates build up to around 40ppm you can perform a 30% water change to lower the Nitrates.

You can cycle your tank with your Axolotl in the tank but you must make sure you test daily to ensure your Axolotl doesn't become exposed to high concentrates of Ammonia or Nitrites.

You can read more about 'Fish-in' and 'Fishless' cycles in these articles:
Caudata Culture Articles - Cycling
How to Cycle a Fish Tank
Caudata Culture Articles - Water Quality

For articles on housing, feeding, biology, health, read the articles within these websites:
Axolotls: The Fascinating Mexican Axolotl and the Tiger Salamander
Caudata Culture Axolotl Articles

As for the substance that has appeared in your tank, I'm not sure. I've not seen anything like that produce within a tank. It looks like decomposing pellets, or some kind of mold..
Perhaps someone else has seen this before that can advise.

I think it would be safer to remove your Axolotl and keep it in a large tub/container. Change the water 100% everyday in the container with dechlorinated water so the Ammonia levels to not build up. Then I would remove the sand in your tank and rinse it again.

Make sure to rinse the sand thoroughly. I use a pillow case and fill it with the sand, then run water through it for some time.

What filter are you using? and how big is your tank? it may be the filter is suitable and will provide superior filtration even if it is for larger volumes of water.
What dechlorinator are you using also?

Thank you for your prompt response. I read it the day you posted but have been too busy at work to respond.

I promptly purchased the test kit you recommended online but in the meantime have been using the strips. According to those the nitrate, nitrite and ph levels are adequate. Kh is at 40 which is listed in the CAUTION section and gh is 180 which is also under caution. I also had a petsmart rep test the water the day before yesterday thinking they would have something more accurate than my strips but they didn't. The petsmart rep said that the high gh is average for our county and voiced that foggy water isn't necessarily something to worry about but I am still concerned.

As you said, these strip results may not be very accurate as the water has become foggy and smelly and sounds exactly like new tank syndrome.

I have been changing 30% of the water daily. I will now be changing 100% as you recommended since I am currently in crisis mode even though my question concerning that is...don't I need to keep a bit of the water in there so that it'll start developing the ideal bacteria? Yesterday to address the fog I put in some clarifier that I had purchased awhile ago but today it is more foggy and when I got home tonight my axolotl was swimming up to the surface which I know is bad.

I thought that maybe in-cycling was a possibility but at least for the time being I have removed him from the tank. I hadn't done this earlier as I don't have a large container but I will be keeping him in a bucket for the time being and changing the water 100% every day as you've recommended. I read online that if I were to do in cycling which is definitely the long term goal here I should feed him as little as possible. Is that correct? I will continue to read the resources you provided which have been very helpful.

As for the substance they do look like pellets but I feed him blood worm cubes.

When I cleaned the sand I sifted through it in a buckets
of water around 6 times until the water appeared clear but I will be using your pillow case method.

I have an aqueon filter from petsmart, the tank is a Size 10 glass aquarium 20L by 10 inches width by 12 inch height, capable of holding 8-10 gallons of water. As for the bigger filter I had to toss it because it stopped working. The dechlorinator I use is tetra brand.

Another question, the filter directions recommend running the filter under cold water but this water would have to dechlorinated first, no?

What does the grey stuff feel like? Is it hard or soft, that would most likely give you a clue. And remember that axies HATE current, it's bad to have them exposed to it. So make sure you divert it with plants or decor