probably not necessary, if you're using good soil, and your water is relatively soft. Soil-type meters are fairly inexpensive, if you're concerned about your soil condition, buy one. These are acid loving plants, gradually walking the ph down during flowering would be the fine-tuning. Good Fortune to Your Grow!
They're not even expensive, and in my opinion they're pretty essential unless you're an experienced gardener. It's VERY easy to fuck up the pH and cause a bunch of lockouts, and they're too cheap to try and skimp on buying one. You can get a hanna pH meter for $28~, and if you put the 4.01/7.01 testing solution 10ml packets in little clean bottles you can wait awhile until needing to buy more calibration solution.