pH Test? 3 drops in 5ml. (ideal range 7.1-7.6) NB. The black gravel in there is constant buffer so should be no need to use any coral sand. If you get a below 7 reading consult Bruce first. As it is white, coral sand or she'll grit should not go in directly to the tank
Though possible this is fairly unlikely just on the gravel alone. Rinse test tube thoroughly and retest. (Any traces of AMMONIA TEST or GH TEST solutions will give a false alkaline reading) If still high then we must assume that there has been an excess amount of coral sand and all we can do is water change. It will eventually come down as the coral sand dissolves.