Fertilizers are a very complex subject that do require some knowledge of chemistry sorry, Diane! and are not my area of expertise, but for the hobbyist orchid grower a basic knowledge of pH and TDS applied to your growing regime can go a long way to making your plants very happy, and possibly urging those stubborn bloomers to strut their stuff.

pH

pH is a measure of the hydrogen ion activity in a liquid. That sounds like Greek, so let me rephrase it: pH is a measure of acidity. The scale runs from 0-14. Zero is caustically acidic, and 14 is caustically basic that is, acid vs. base. While living organisms can specialize microclimates of high acid low pH or high base high pH, they themselves typically must live in the middle of the range, where things aren't too nasty. Our stomachs are great examples. Gastric acid has a pH of 1.5-2.0 quite low on a scale of 0-14... When everything is working fine, we don't notice, but if you vomit or burb up stomach juices eww! the acid burns your esophagus, which isn't prepared for the acidity.

Just for fun, here are some typical pH's:

-.05 Battery acid
2.5 Coke that's scary!
3.5 Orange juice
5.0 Coffee
7.0 Pure water
7.35-7.45 Blood
8.0 Sea water
9.0-10.0 Soap
11.5 Ammonia
12.5 Bleach
13.5 Household lye

Not only will an incorrect pH burn our plants if it's wildly off, more importantly different nutrients will dissolve or precipitate out at varying pH's. That's to say, if the pH is off, a nutrient may be in your fertilizer, but your plant's not getting it. I think the latter point is the more critical one for orchid growing.

Handheld pH monitors are commonly available in the $20-30 range.

TDS

TDS stands for total dissolved solids in a liquid, and is measured in parts per million PPM. These 'solids' can include salts, minerals, metals, cations and anions.

They aren't good for us, or our plants, and orchid are particularly choosy about the quality of their water. If it's good, they'll grow like crazy! The common ways of filtering or removing solids include: reverse osmosis R/O, deionization, microfiltration, distillation and carbon filtration.

On a PPM scale, here's what TDS looks like:

0-50 'Pure' drinking water, acheived through R/O, deionization, microfiltration or distillation

50-160 Carbon filtration

170 Definition of 'hard' water

160-400 Average tap water

500 EPA's max contamination level

So you can see that our tap water is pretty disgusting. Handheld TDS meters will measure TDS. You'll also see electrical conductivity EC meters available. They get you to the same place. In fact, they're one and the same thing. The only real way to measure TDS is to evaporate a water sample and weigh the junk that's left. TDS meters use the electrical conductivity of a solution to work back to the total dissolved solids. Good meters are as low as $35. PM me if you'd like sources.

Orchids care greatly about TDS. They want fertilizer, but high salt levels will burn their leaves - badly, depending on the orchid. You want your water as pure as possible, and the right balance of fertilizer for your plants. If water doesn't flush the pot regularly, or if the plant dries out too much, all those salts get concentrated in the leaves and roots and burn 'em! To alarming degrees when serious. You simply don't know what's going on in the pot, without the ability to measure it.

When watering, or soaking a plant, stop your sink or use a bucket, so the runoff water leachate doesn't escape. Then test the TDS of the leachate. That will tell you what you're doing to your plants.

Ok, those are the basics. I haven't gotten into ideal leachate TDS, because I haven't figured that part out yet...

But I'll repeat a link that Steve pointed us to, because it converts fert levels in tsps/gallon into TDS:
Fertilizer Calculator

Happy growing!
Julie