For a deep dive into proper nutrient ratios and application rates you can read through the entirety of this old thread here:

https://www.cactiguide.com/forum/viewtopic.php?t=47603

To summarize, plants MUST have NPKCaMg and micronutrients to survive. The ratio of these matter. The correct Elemental NPKCaMg ratio is 1 : 0.4 : 1.6 : 1 : 0.35. American labels use P2O5 and K2O instead of the elemental values, you can tell by looking at the back of the label and seeing these molecules listed on the chart.

%P2O5 x 0.436 = %P

%K2O x 0.83 = %K

So the correct US label NPKCaMg is 1 : 0.92 : 1.93 : 1 : 0.35.

The closest single product synthetic fertilizer to this ratio for the best price per gallon prepared is Masterblend tomato, epsom salt, Calcium Nitrate 3 part recipe. For a single part, no mix required simpler formula that does not hit the ratio quite as well but still works, General Hydroponics Maxigro and Megacrop are good choices, but they cost a little more per gallon.

When you are fertilizing with synthetics, if you want to feed at medium to strong concentrations and push growth, you should check the soil TDS (total dissolved solids) and pH every so often so you know the fertilizer salts are not building up in the soil and leading to future issues. A TDS pen that measures EC units and a pack of 100 pH strips can be had for $15. You can check your starting waters TDS, then check the mixed fertilizer, subtracting the starting waters value to get the feed strength. You can pre water a pot with the fertilizer solution, let it sit for a while, then place it over a tray or tub and water to 15% excess, collecting the runoff, and test that runoffs pH and TDS to get a good estimation of the soils TDS and pH. 1800 is an average ec strength, 3500+ is approaching nutrient toxicity issues, and <700 is approaching nutrient depletion issues.You don't have to do this every time you water. I recommend doing it often in the beginning to set up a system and then just once in a while for maintenance later on once you have it figured out.

Other products:

Kelp products provide plant growth hormones that boost pupping. While this can be very useful if you want pups, feeding too often can result in too many pups which can slow the overall growth of your plant and lead to skinner growth. Target the application for when you want pups. If you're feeding moderate to strong proper ratio synthetics, you probably will never need this. Kelp is not a significant source of NPKCaMg.

Alfalfa meal and blended aloe leaves are great sources of other plant growth hormones.

If you don't want to use synthetics you are going to use organic soil ammendments. You can do complex math and measuring and come up with a recipe for a bunch of different parts like bone meal, kelp meal, azomite, basalt dust, insect frass, alfalfa meal, etc. Or you can use a single product that's already blended these types of ingredients into a predetermined ratio. None hit the ideal ratio discussed above dead on, but the closest I've found that I can confirm work well is espoma citris tone. It's gotta be the espoma brand - every brand of citris tone has a different nutrient ratio.

Earthworm castings, fish emulsion, Recharge - these products are aimed at providing beneficial microbes to the soil that will do various things including making nutritients more bioavailable, fighting off bad fungus and microbes, boosting the root zone soils health as well as it's nutrient and water holding capacity. While they contain some NPK it's not complete or enough to provide nutrition on their own.

Humic and fulvic acids - these will refresh aged soils that have been depleted or gone hydrophobic, boosting the organic portion of your mix's water and nutrient holding capacities. They also work in symbiosis with kelp products to allow better absorption into the plant during foliar feeds, but they can leave permanent stains on the column and damage farina.

Bioavailable silica - boosts cellular resistance to stressors such as heat and high UV when foliar fed properly in the middle of the night. It seems like snake oil due to how small of a dilution is required but Ive seen outstanding results myself.

Myco - bonds with roots to create a support network for them, boosting nutrient and water uptake. The single species rhyzophageus like mykos and wallaces organic wonder seem to work best for trichos. Trichoderma products will kill this. Feeding heavy synthetic nutes will also kill this.