Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Try one. If the sand is deep enough then you should not be able to test any rising nitrate.
If the sand is allowing more water to flow around the capsule then your tank will show rising nitrates.
Of course the plants may use the NO3 from both substrate and water, so the test shows little or no nitrate rise that you could blame the capsules for.