(I) The level of feed which a plant can take depends on the amount of light it is getting - foot candles (or lux) x daylight hours i.e. June 21 needs twice the feed for Dec.21.
(2) Do not feed heavily unless the plant is growing well.
(3) The more you feed the quicker the compost rots. If using more than 400 then bark needs annual replacement.
(4) An important use of the meter is to check the conditions inside the pot. Immerse the pot in plain rainwater, allow most to drain, then collect the last drainings (an eggcupful) and take a reading. If it is very high - repot. If it is merely higher than used as fertiliser do not feed, just flush at each watering until the reading comes down.
(5) Disas should be fed weakly i.e. below 200 and even then use rainwater or low levels for 90% of the time.
(6) Dendrobiums can stand 200 to 300 but must be flushed with plain water before being dried out for the winter - if they are that kind.
(7) Paphs will take at least 300 all the time going to 500 during the summer.
(8) Odonts. need very little, say below 200 if grown cool and dark and up to 400 if grown intermediate and bright.
(9) Most terrestrials and semi-terrestrials e.g. Calanthes, Cymbidiums will take 500-600.
(10) Phals. are supposed to be high feeders and will take 500-600, but take care.