pH drop in established tank

[Naughts]

I have been doing the water changes every week and it goes up with the fresh water and 4-5 days later it's back in the low 5's. I have tested my water source and it was 7.4pH

The planted tank would be around 35% of the volume.

When you test your tap water it is recommended to let the water stand for 24 hours. This is because water companies sometimes add temporary pH buffers to prevent acid corrosion in the pipes. If this is the case, the reading straight from the tap will be inaccurate.

 

[Avel1896]

When I was using tap water, I let it stand for 72h.