Seedlings stopped growing.

I have grown a lot of different plants from seed but there is a challenge I encounter with many cactus and succulent seeds. At around the size of a dry pea they stop growing. Eventually some bounce back and start growing again but some never do and eventually die. (currently I have some frailea I started in 2021 the largest is about the size of a dry pea the rest about the size of peppercorn.) So I'm looking for any advice to improve seedling growth. I will provide as much info about my current growing conditions as I can below.

I live in Chicago and so I grow my seeds indoor under grow lights until it is safe to move them outdoors the next summer. I started a variety of different seeds over summer all have stopped growing. I started them in a humidity tray in builders sand washed out with a sieve so its fine but not compact. (In the past I used coconut coir but stopped do to mold and plants damping off.) I left them in the humidity trays until haworthiopsis, psudolithos, &, Whitesloanea crassa seedlings started dying about 5 months later. After that I took them out and cut back on watering to twice a week. PH of water is about 6.3 Temperature average around 72°F/ 22°C. Fertilizer I started with was Bonide Liquid Cactus Plant Food, but I switched to Liqui-Dirt a few weeks ago. (I haven't noticed any change)
Light - Cresmar P1200 LED Grow Light. Light is on 12 hours a day. The lighting varies depending on their position:

120 µmol/m²/s - Psudolithos cubiformis, pseudolithos migiurtinus , Whitesloanea crassa, & Pilosocereus leucocephalus
The Psudolithos & Pilosocereus appear a heathy green color. The Whitesloanea looks kind of yellow/brown looking, not sure if that's normal for it.

70µmol/m²/s - aloe hybrids
They look sun stressed, but I am not very worried about these since I grow a lot of aloe and they always start growing again in Summer.

40 µmol/m²/s - aloe hybrids, & haworthiopsis
These aloe hybrids look healthier.

Since no other people have responded I will do so, but I break nearly every so called rule when it comes to these plants. However I do so out of knowledge and experience. I've been doing this a long time and have refined my methods for over 20 years.

First, the plant food issue:
I tried to find the NPK of Liqui-Dirt. I was surprised to learn that the company is local and not that far from where I live. On their website I couldn't find a listing for the NPK of the fertilizer. I found this

So, first everything is made of chemicals, there is literally no substance in the Universe that is Chemical-Free. Hydrogen is a chemical element, for example. So automatically I can see that the claim was either written by or for ignorant people.
Then there is the claim that Liqui-Dirt won't burn or harm plants but synthetic fertilizers will. Legitimate fertilizers of any type can burn plants, it doesn't matter if they are organic or synthetic in origin. I've used a lot of organic fertilizers, but I also use synthetic fertilizers and have for about 30 years. They don't burn or harm plants when used as directed.

Here is another quote from their page:

I can't argue with that, but if they meant to write fertilizer, this indicates that Liqui-Dirt is not in fact a type of plant food.

And then there is this:

Again, we see that this is being marketed to people by people who have no idea about the needs of plants. What the product appears to be is a form of plant vitamins. Imagine trying to survive by eating vitamins without food! That is not much different than what they are trying to sell.

As for Bonide Liquid Cactus Plant Food, it isn't a product I can recommend. I use an even ratio of NPK, like 20:20:20, though I dilute it and generally use 1/4 a teaspoon of 20:20:20 per gallon of water. I don't use any plant food marketed for use with cacti. Nearly all plants have almost identical nutritional requirements, even cacti. This is because despite their distinct visual differences when it comes to their cells plants are all quite similar.

Next, humidity and air flow:
I also keep lids on trays for germination only, if the seeds all germinate then I remove the lids right away, otherwise I give them 2 weeks at most with lids on.
Plants obtain carbon from the air, they use this carbon to make sugars, which they use for energy and use as building blocks. Plants also require Nitrogen to do this, as well as Potassium and Phosphorus, but they also often have a strong need for calcium and magnesium. Plants need plenty of light, air, food and water to grow. Methods that enclose seedlings in containers that maintain humidity suffocate them and this strongly limits growth and decreases their ability to tolerate light. They are useful methods in how they allow a person to neglect the seedlings and still have them grow, but if attention can be paid to the seedlings on a daily or near daily basis then the methods using prolonged humidity are probably the worst option for growing seedlings that there is.

Next watering and the Pump Sprayer:
I recommend a pump sprayer for feeding and watering and making sure that the soil does not dry out when the seedlings are small, this is a really useful tool for this. I use a 1 gallon size. I recommend feeding the seedlings before they actually germinate, a little bit of fertilizer actually helps them germinate and grow in many cases. I try to maintain a constant level of fertility by ensuring that nearly every time I water that the water has plant food in it and I avoid letting the mix get dry until the seedlings are well established.

Next day length and light intensity:
When seeds first germinate I often use a 12/12 schedule for light/dark, but as they grow I change it to 16 on and 8 off. This produces considerably faster growth than 12/12 does, especially with plants that use CAM or Crassulacean Acid Metabolism.
I also ignore things like red and purple pigments in seedlings of cacti, despite widespread misconceptions about these pigments they are rarely a sign of excess light and can show up under very low light levels. The pigments are also quite common on healthy seedlings growing well.

Next light choice:
I use LED lights build to illuminate rooms, not grow lights. Especially not grow lights with purple and pink colors to them. The closer to sunlight in CRI and degrees Kelvin the better. When I have used an app to measure light intensity it is typically near 26,000 lux, bright. I give them as much light as I can without overheating them.

@Floraleo
Thank you for replying.
I usually use Dr. Earth fertilizers but the organic matter grows mold and I am trying to prevent damping off. My first two attempts to grow Pseudolithos from seed ended after about two weeks when the plants changed color and rotted away. Also had a batch of Adenium seedlings die after a few months. That’s why I was looking for an alternative while the seedlings are still young and vulnerable

So I tried Bonide but I wasn’t sure if it was providing all the proper micro nutrients since it only lists NPK. This is why I tried Liqui-Dirt, I never looked at their website. Just found it browsing amazon, and I tried it because the product was already decomposed so I figured there would be less of a chance of mold growing, and it had the micro nutrients listed on the back packaging: https://m.media-amazon.com/images/I/81FOTaYAdaL._SL1500_.jpg
I don’t know if the percentages are ideal. But it said on the amazon page: “There is no need to mix with other fertilizers or systems. Liqui-Dirt is all you need.”
You didn’t say what brand of fertilizer you use, Do you have a fertilizer you recommend for seedlings?

Also some members on another forum recommended repotting the seedlings in a mix that is equal parts sand/pumice/organic to provide better nutrition, So I am trying that with some of the seedlings.
Usually I don’t keep seedling in humidity trays for more than a few weeks. But I had read on another websites people claiming they leave Pseudolithos in humidity trays for around a year. Which was why I left them in for so long.

Yes, I do use a one gallon pump sprayer to water my plants.

I will see if increasing the light hours has any impact. I don’t currently have a lux meter so I bought one and will compare when I receive it.

I use Schultz 20:20:20 at 1/4 tsp per gallon.
Sandy mixes work well.
No real need for a light meter, just keep it bright but make sure the lights aren't close enough to cause over-heating.

Thank you Floraleo, I will try increasing the hours of light and try the Schultz fertilizer and post back at the end of the month with the results.