@SlowMovingWaters
Trees can't read labels. Brand does not matter. But the analysis does matter.
What are the numbers on your fertilizers?
Ideally, fertilizer should be chosen to compliment your potting media and water quality. Trees use nutrients year round in roughly the ratio of
12-1-4 and require calcium at 12, magnesium at 4, sulfur 2, and a long list of micro-nutrients.
However plants accumulate and store some nutrients, and the potting medium has some capacity to store nutrients (the CEC ). If nutrients are not balanced to the plants needs, a flush with clear water will help flush out excesses of nutrients. Since we tend to fertilize episodically, rather than continuously, you can pretty much get away with using just about any fertilizer.
The fertilizer with the least amount of waste will be 12-1-4 or a 12-1-13.
Most commonly available fertilizers are 30-10-10, or a 15-5-5, These are not bad, and can be used.
If you use a 10-10-10 understand that it is NOT balanced to the nutritional needs of the plant. Yes the numbers are the same, but this does not mean it is balanced. Humans need a large amount of vitamin C every day and very small amounts of vitamin D. If we consumed vitamin D at the same rate we consume vitamin C, serious health effects would harm us. One can die of vitamin D poisoning if too much is consumed.
Similar with plants they do not take up nutrients at the same rate. The ideal ratios are roughly as above. 12-1-4. Note, there are several forms of nitrogen, the first number, when the nitrogen is primarily as nitrate the last number potassium ( K ) should be equal to the nitrogen number, because the plant consumes K in order to absorb N. So a nitrate based fertilizer should be 12-1-12, where an ammonia based or urea based fertilizer should be 12-1-4
How strong should your fertilizer solution be?
It depends on the stage of development of your bonsai. A young tree you are trying to bulk up, get to grow rapidly, the fertilizer should be at label recommended strength. However, for intermediate and advanced bonsai we do not want rapid coarse growth. We want slower, finer growth with short distances between leaves (leaves are at nodes, we want short internodes). Full strength fertilizer will create long internodes, long distances between leaves. Generally fertilizer labels recommend concentrations at a strength intended for vegetable gardens. For bonsai use should be around 1/2 to 1/4 the "vegetable garden strength".
So, use your fertilizer, brand doesn't matter, the analysis numbers matter. Generally without knowing the analysis I would say 1/4 to 1/2 strength, would be safe. Fertilizer frequency should be as
@BrianBay9 suggested.
There are many more details and nuances to fertilizer, but I have typed enough for now and you are probably tired of reading at this point.