I am setting up a 2nd system and cannot get either bacteria to appear. 100L hydroton flood/drain barrel system. Fishless cycling, ammonia @ 2ppm PH keeps falling. PHdown to the rescue. Still no results for weeks. Tried boosting to 4ppm and 5ppm but still no results. Ammonia keeps falling and so does Ph. South forida system so temperatures are in the mid-70's to mid 80's. Plants are growing like crazy. tomatoes everywhere but will not turn red. Ugh! I read everywhere to just be patient these things take time. I set up the system just before new years, and still no fish. Most posts about cycling seem to be the generic instructions for cycling not too much troubleshooting. Maybe if the Nitrites showed up I wouldn't be so impatient. Anyways, I was looking for any insight anyone might have as to my situation.
Current PH: 6.3 Ammonia:4ppm Nitrate/Nitrite: 0ppm Temp: 77degrees
Got another test kit to make sure that wasn't the culprit.
If ammonia goes down to none, you must be at least partially cycled. In my experience, it's not unusual to see 0 nitrite in a cycled system - my system has lots of media filtering and 0 nitrite is normal. Low nitrate can mean that the plants are taking it all up but testing none at all is odd. You must be careful with the nitrate test to add the first regent, shake for a minute, add the second regent, shake for 5 minutes (API).
If your ammonia was falling and PH too, why was it necessary to add PH Down? This sounds contradictory.
If your system is cycled then PH should fall as nitrification occurs. At that point, it is generally necessary to raise PH, not lower it. If you are having to raise PH, that indicates that your system is at least partially cycled.
Plants growing like crazy seems to indicate they are taking up nitrate, which means you are cycled.
Other than what you wrote about PH, my guess is that you are cycled. I suggest you simply monitor ammonia to be sure it goes down and raise PH when necessary. If those two things are happening, you are cycled.
Conventional wisdom is that a fruiting plant, like tomato, is difficult to grow in a new system. However, it seems to me that if you have green fruit, they should ripen. However, I don't usually grow tomatoes in aquaponics so possibly someone else can speak to this.
Also, things will go a lot faster if you bump your pH to 8.0-8.6. Nitrifying bacteria love it in that range. (Once you get the results you're looking for and are ready to add fish, lower it back down again)
Like George said, if your ammonia keeps dropping, and you're not getting any nitrites or nitrates showing up in your test, then the plants are probably doing their job and you're done cycling. The ammonia has to go somewhere.