25-5-15 High Proformance Fertilizer manufacured by JR Peters Inc. It has the perfect nutrient ratio for citrus. However, it only comes in 25-lb. bags. If you only have one or two trees it might be a little much for you.

Foliage Pro 9-3-6 is another good fertilizer for citrus and it comes in smaller sizes.

Are these indoor or outdoor trees? Do you know what sort of soil you have? Knowing the PH or general level of acid/base in the soil along with nutrient levels would help. Everyone seems to have their favorites but "Dyna-Grow Foliage Pro" which is 9-3-6 and seems to have a lot of fans. I have somewhat basic well water so I use "JR Peters, Jack's Classic Acid Special" which is 17-6-6.

I've read 9-3-6 is the ideal N-P-K ratio but they should do well with any quality high nitrogen fertilizer.

I like foliage pro but my plants do much better with the jack's acid special in my growing conditions(Zone 5 potted plants with well water). I wouldn't worry too much about getting "the best" fertilizer as what's best depends on your specific conditions.

Mine is indoor with just a regular potting soil mixed with perlite. I have no idea what is the PH level of the soil as I've never tested it.

The pH soil of tap is more important than pH of your mix. pH of your outside soil would matter greatly if your trees were in-ground..It is easy to find out what the pH of your tap water is..