Easy Carbon lowering pH? Tips for buffering hard water? Tips to stop overthinking this?

[Katya]

My five-gallon tank had a pretty consistent pH of about 7 for a month (using test strips near daily as I was cycling the tank and introducing the fish).  Nitrates and nitrites consistently low.  No wasted food -- we have one betta and feed her in her floating log, so any uneaten food (ha!) would fall to the bottom of the log, never the bottom of the tank.  I have about five live plants, dosing with fertilizer (started with Seachem Flourish, but noticed pinholes in one plant, so switched to Easy Green to add potassium).  Lights on only 8 hours a day (on a timer, with four hours on, two hours off, four hours on).  The tank is a Fluval Spec V with a coarse prefilter over the jet to buffer the flow for the betta.  Weekly 20-percent water changes.  (Sorry if this is too much detail; I'm not sure what info might be relevant.)  

I was getting algae on the glass, the rocks and driftwood, and the plants, so I began dosing with Easy Carbon.  Now my pH is starting to test lower.  I'm including a photo of today's test strip.  My tank has always had low buffer, but my water is hard.  I can't find crushed coral in one-pound increments (the co-op is out of stock) and don't want to buy 10 or 15 pounds of the stuff for my little tank, so I'm trying Seachem Neutral Regulator to try to gradually bring the pH back up and hopefully buffer the tank.  But I'm moderately concerned because the Neutral Regulator apparently precipitates minerals out of the water -- will it do that if the pH is below 7, or only if the pH is higher? Will that cause a problem for my fish or my plants? 

I don't want to get in a cycle of adding chemicals to counteract the effects of other chemicals.  Could Easy Carbon be lowering the pH?  Is there a level below which it won't lower the pH?  (That is, is there a floor to the pH reduction?)  Is there another reputable source for smaller quantities of crushed coral?  Is there another way to increase the buffer in my tank?  Am I overthinking all this?  (The last option is very likely!)  

[Colu]

You can use crushed Oyster shell as an alternative to crushed coral