phtest

I saw that these were on sale and decided to buy since I don’t own one yet. Which one is the best to buy?

40 gal dis. reef w 20 gal sump 2/27 Ph 8.2 DKH 11 3/4 PH 8.3 DKH 10 3/10 PH 8.3 DKH 10 3/14 Ph 8.3 DKH 10 3/14 Added G Bubble tip anemone and small drag of GSP 3/15 Ph 8.6 DKH 10 ( 10 gal water change after 8.6 reading) 3/16 Ph 8.6 DKH 10 Calc has stayed at abt 490 ppm Haven’t done anything...