Decreasing PH is a sign that you bacteria are hard at work. If you look on your PH UP bottle it will tell you the raw ingredients that are at work. Potassium bicarbonate may be one of the things on the ingredients and you can buy that on ebay or a beer brewing supply website. That is a fast acting one so good for now. In the future you may want to use something that is slower acting but longer lasting like calcium carbonate (egg shells or shell grit) There are others that are Hydroxides but they are not considered "organic".
...or that your pH down is hard at work...
pH 8 -8.2 is a great pH for fish-less cycling...should've just left it alone instead of doing the 'Elvis roller coaster'...
So what exactly is in that bottle of pH UP...since there not all the same...?
You can make your own potassium hydroxide with nothing more than rain water and ashes. It's super easy, skill level 1 type stuff...and about as "organic" and "sustainable" as it gets IMO...
Vlad, I'd be interested in seeing that DIY recipe for potassium hydroxide Vlad
You need a (small or large...it doesn't matter) barrel (plastic or wooden...absolutely no aluminum or galvanized steel) with a spigot near the bottom. Some sort of mechanical filter (I use some pH neutral rocks and some straw. A couple inches of rocks in the bottom of the barrel and 3-4 inches of straw atop the rocks). Ashes from hardwood trees (like Oak, Elm, Locust etc...no pine trees). Dump the ashes over top of the rocks and straw. Put in your rain water (de-mineralized/distilled water works too...just don't use tap water. It's really important that the water be as free of minerals and bicarbonates/alkalinity)...Let it all sit for a half day, a day (it doesn't really matter). Grab a plastic bucket put it under the spigot, and open the spigot. Collect the water in to the plastic bucket. Close the spigot. Pour the water from the bucket back into the barrel. Repeat the process of filtering that water through ashes until you arrive at the desired strength (pH).
Soft, aggressive, mineral free water will leach the potassium from the ashes and leave you with KOH. The rocks and straw do nothing chemically for the process. Again, they are just a filter to keep the ashes from clogging up the spigot.
Calcium Carbonate and potassium carbonate