Try Tom Barrs formula with 50% water changes weekly, much cheaper and
simpler than screwing with test kits. With only a bit of adjustment you can
work out what is best from that point.

Yes, that's the way to go. One point though, get your tap water tested
so you know where you're starting from for the purpose of adding ferts
is to bring your levels up to where youwant them to be from where they
are.

Some tapwater is high in phosphate so you wouldn't want to add any
if it's fine out of the tap. If your water is very hard you won't
want to add MgSO4 ("Epsom salts"); if your water is soft, you do.

Once you know the difference between where you are and where you
want to be it should be easy to figure out what to add each week.

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