Water Hardness and PH

[pezcaito]

Hi all!
I have a 30 gal tank with mostly brackish fish but I don't add any salt. It has a regular filter that hangs in the back of the tank with activated charcoal and I run a powerhead pump every few days to move the water and it helps keep the water clean. I also added some Pothos plants and a moss ball to help clean the water. I don't do water changes often, maybe once every couple of weeks, and I add water every week.
It seems like my nitrates and nitrites are great, however the GH high and KH is low are confusing me and the PH is rather low. I know that the city has increased the PH to over 8 to stop the pipes from leeching lead until they are able to replace all the galvanized steel main pipes that have some lead in them.
The first picture is the water in my tank, the second is my tap water. The tap water has a high KH high PH and low KH.
My fish seem fine, I haven't had any fish or snail die except for the ghost shrimp that are either hiding or someone's been eating them.
IS my water ok, do I need to do any changes?

Thanks

[charliebankston]

Nitrification does have a side effect. A couple of free hydrogen ions (H+)1*are produced for each molecule of ammonia processed, and hydrogen is the “H” in pH. The importance of a stable pH in aquatic systems is also common knowledge. The acidity or basicity of water affects everything from fish respiration to the availability of nutrients and minerals for plants. And hydrogen ions drive pH down - make it more acidic.2*The more nitrification activity you have, the faster your system’s pH will drop.*from Aquasprouts.com

[charliebankston]

Basically, more waste in the tank, more nitrification, and lower pH. More frequent 25-33% water changes will help

[pezcaito]

Right but the Nitrates and Nitrites are super low so I don't get it.

[charliebankston]

Yeah, the plants are helping take out the nitrates. And the nitrites are being converted to nitrates. But that process is helping lower your ph too

[charliebankston]

Just try a weekly water change of 25% for a month and see. Test after the 4 changes is up and compare to now and then you'll know if that's your culprit. Replacing evaporated water doesn't count either, lol

[pezcaito]

I checked the filter, there is no gunk in the cartridge, I haven't cleaned it for weeks. What's up with that? Seems like there is no bacteria or algae buildup.