PH Keeps dropping. Are my readings false? Am I able to test PH after adding substrate

[jblasto]

I just set up and planted my aquarium using a substrate called aquadurt. I have a PH probe that runs out of my sump back up to the tank and it keeps showing a steady drop of PH over time from when I put clean water in (7.9) from the tap which will drop to around (4.9) after about 8 hours. The guys at the pet store told me that the probe will give false readings until all the particles from the substrate settle. That the probe is reading the cloudy water and miscalculating the PH. How long should this last though? The tank looks relatively clear. It was planted yesterday and although it was indeed cloudy afterwards seems like these results should return to normal? It also seems crazy to me that me filling the tank with 7.9 water and it shifting to be that (4.9) acidic over and over is impossible. (I have done huge water changes three times before calling the store which was when they mentioned the high likelihood of false probe readings).

My concern is that 4.9 PH (if it is accurate) is too low for the plants. I need at least a ph of 6 and thus means I need to keep doing water changes. Any advice such as "leave it alone, it will return to normal readings in a week after settling"? ... or "Keep changing the water! It will kill those plants!" heh... Thanks.

[emc7]

Many plant substrates have peat-like stuff in them that will drop pH, so will CO2. Take a sample from the filter output and test that. Double check with a liquid test, they are cheap. Low-pH isn't incompatible with planted tank, many tanks with CO2 drop down when it is on and go back up when it is off. I'd only worry about the fishl

[TheOldSalt]

Stop changing water and wait to see what happens. If it really IS dropping the pH that much, then the last thing you need is the rollercoaster effect.

[emc7]

Are you cleaning the probe? It sounds great to put it in and leave it in, but accuracy may require both cleaning and calibrating. Do you have standard solutions?

[kcrunch]

There is a substrate on drfosters that is called rift lake sand it is a whitish color it will surely keep your PH balanced

[lohachata]

any time you are using test equipment it needs to be cleaned properly...that means washing and rinsing it with deionized water and allowing to air dry...
probes need to be constantly calibrated...that may well be the problem..