A useful trick to find out what it is like in the pot ( non S/H) is to water as usual, and collect the last spoonful or so of water draining out , and then check the EC and pH of that. If you had put water in at say 600EC, and the collected drainings are at 900 EC there must be unused strong fertiliser solution ( or newly dissolved crystals) in the pot – and you know that flushing is necessary. If you put water in at pH 6.3 and the drainings are pH 4.5 you know that the compost has gone sour and re-potting is overdue .If they came out the same as they went in, all is well.
To correct, lower pH, yes you need acid. For small quantities lemon juice or vinegar. To raise , try household ammonia. You can get stronger specialist stuff from hydroponics or maybe aquarium suppliers ( aquarists are interest d in adjusted water quality too ! ) Look for “pH Down” or “pH Up” . Down is usually orthophosphoric acid – good stuff for orchids as the Phosporus is a useful boost. Don't use straight from the bottle - too strong ! See my other posting about this.
Transition times ? Every time you change the compost or potting media type, the plant needs new roots, because the physical root structure adapts to the material it grows into ; once fixed it can’t change those roots. So changing media frequently is a certain recipe for disaster . A good plant has live and useful roots from the last 4 years….not ones from this year and less useful or even useless ones from years,
S/H means an abundant supply of water – everything else must be up to full capacity too in order to use that – like is the plant as warm as it wants to be, or are you operating at the extreme range of possibilities – ditto, and the same for light. Everything in balance - that’s what a healthy plant needs !