ok lemme see if i can explain this without confusing u LOL (i have that way about me) you never have to use the high ph unless your ph is over 7.6 ....the reason you are getting a 7.4 on the high is because it doesnt go lower on the color chart with the high test bottle......but in reality, your ph is 6.4(if you had a yellow 6.0 reading on the low side, it means that it probably is below 6 and you cant tell because thats the lowest it goes) ....does that make sense?
so back to the original question..your ph is 6.4 and your
ammonia is 1.0 with no nitrates..which means you are just at the beginning of the cycle process and need to do daily water changes until you have 0 ammonia and nitrites and under 20 nitrates because you have fish in the tank..either that or get some tetra safestart or established media off another tank thats been completely cycled for a month or more ...did i confuse u?