A hydromoter is highly unrepeatable. Little bubbles may throw it off and you can not calibrate it. A refractometer is much more repeatable and you can calibrate.
As far as kits, I would go for the following:
Ammonia
Nitrate
Nitrate
Ph
Phosphate
Calcium
Alk
Magnesium
My preference is Salifert and the cheapest prices that I have found are at Aquatic Technology (Cleveland Area). They do mail order.
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