Your pH of 6.0 is the most urgent problem.

Critical Issues

Your pH of 6.0 is the most urgent problem. This is dangerously low for virtually any freshwater aquarium, and it is almost certainly the reason your cycle is stalled. The nitrifying bacteria responsible for converting ammonia (Nitrosomonas and Nitrobacter species) become severely inhibited below pH 6.5 and essentially stop functioning below pH 6.0. This explains exactly why your ammonia is sitting at 0.50 ppm with zero nitrite and zero nitrate, which would normally indicate an active cycle producing those byproducts.

Your tank is not cycling. The bacteria cannot do their job at this pH.

Secondary Concerns

• Ammonia at 0.50 ppm is not immediately catastrophic with no livestock present, but it will not convert on its own until pH is corrected.
• A bubbler alone may not be providing enough surface agitation for efficient gas exchange, which can contribute to CO2 buildup from plant respiration at night, further pushing pH down.
• Zero nitrate in a planted tank with rising ammonia is consistent with plants consuming some nitrogen, but plants cannot keep up with unchecked ammonia input, and they cannot fix the pH problem.

Priority Actions

1. Test your tap water pH directly from the tap and after letting a sample sit open for 24 hours. If tap pH is normal (7.0-7.6), your tank has an internal acidification source, likely CO2 accumulation, decomposing substrate, driftwood, or organic buildup.
2. Identify the ammonia source. With no fish present, ammonia is coming from decomposing plant matter, uneaten food residue, or a substrate additive. Remove any dead or dying plant leaves immediately.
3. Raise pH gradually using small, measured doses of baking soda (sodium bicarbonate). Add no more than 1/4 teaspoon per 10 gallons at a time, dissolved in tank water first, and retest after an hour. Target pH 7.0-7.4 for a stable cycling environment. Do not try to correct this in one dose.
4. Increase surface agitation by raising your air stone closer to the surface or adding a small hang-on-back filter. Excess dissolved CO2 is a common driver of low pH in planted tanks, and off-gassing it will help stabilize your chemistry.
5. Once pH is above 6.8, add a bottled bacterial starter culture (products such as Tetra SafeStart or Fritz Turbo Start) to reintroduce viable nitrifying bacteria and restart the cycle actively.

Watch Closely

• Retest pH every 24 hours after any adjustment until it holds stable above 7.0.
• Once pH is corrected and a bacterial culture is added, test ammonia and nitrite every 2 days. You should see nitrite begin to rise within 3-5 days if the cycle is progressing.
• If pH continues dropping back toward 6.0 despite corrections, you have an ongoing acidification source that needs to be identified before adding any livestock.