I agree on it's probably a bacteria bloom, which is caused by a different class of bacteria (heterotrophic) than the primary bacteria you're trying to cultivate, multiplies much faster, can multiply in minutes rather than hours. The heterotrophic bacteria aren't all bad, when in balance they break down solid waste and process nitrate.
Some questions are in order. 3 month old tank, but how long has it had fish? What size tank and what's your filtration? Have you changed out any media or have you left it alone? Sounds like water is clear for a while, then clouds back up-- when does this happen? How long does it stay cloudy? Cloudy water for a few hours but then it clears up can happen and isn't really a problem. Staying cloudy is different, often a clue your nitrifying bacteria colony is not mature yet and your tank needs a chance to balance out.
As to pH, the following or similar is well documented in reliable literature:
http://www.bioconlabs.com/nitribactfacts.html
pH
The optimum pH range for Nitrosomonas is between 7.8-8.0.
The optimum pH range for Nitrobacter is between 7.3-7.5
Nitrobacter will grow more slowly at the high pH levels typical of marine aquaria and preferred by African Rift Lake Cichlids. Initial high nitrite concentrations may exist. At pH levels below 7.0, Nitrosomonas will grow more slowly and increases in ammonia may become evident. Nitrosomonas growth is inhibited at a pH of 6.5. All nitrification is inhibited if the pH drops to 6.0 or less. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+ state.
Some basic thoughts:
1. There's a trade-off, ammonia is less toxic with pH in the 6s, but low ph also slows down nitrifying bacteria growth and activity. When you're trying to initially cycle a tank, too low pH slows down the process. Adding bio-load to a low pH tank is trickier than a tank with pH in the 7s in the respect that your bacteria colony responds more slowly.
2. Don't know the history of setting up your tank, but there's a misconception some have about cycling, which is that you reach a point where your tank is "cycled" and you're good to go from then on. Doesn't work that way, what happens is you reach a point of equilibrium between nitrifying bacteria and waste input. Low waste input, small bacteria colony, higher waste input, bigger bacteria colony.
3. This is opinion based on personal experience, not science, but what I learned to do years ago with a jumpy tank is basically as little as possible until the tank reaches a balance. Don't mess with the media unless it's to add some mature media. Do a minimum of water changes, unless an ammonia emergency requires more. Feed lightly. Water clarifier is okay (Acurel is the only one I ever found effective) and can actually help the process ime. Not a requirement, but an option ime. Without getting technical about why, imo heterotrophic bacterial blooms interfere somewhat with your primary nitrifying bacteria, clearing the tank with clarifier (don't overdo it) seems to limit this disruption.
4. All in all a mature, settled, balanced tank doesn't go haywire that easily. It takes some patience to get there if you're getting bacteria blooms, a certain amount of letting nature work it's magic. As Duane says, you can't rush it and panicking and doing
too much can actually interfere.
5. My opinion, again, but jurapari are fine in pH over 7, I don't see the need to keep them in the 6s. I did softwater, low pH tanks for years, but they're not necessary for most fish. Not many fish actually require the same pH as their home territory, most adapt well to a wider range of pH and, in fact, if their native pH is low, unless they're wild caught, the chances are low they've ever seen their low native pH. Nothing wrong with it, but except the few fish that breed better in low pH, keeping a low pH tank is more about being a purist than something the fish actually require.
