Tank as it was when ph dropped
12g Edge Stock Filter/Stock LED lights
Dkh 11-12 Don't want to go higher!
PH WAS HOVERING 7.6-7.8
I took down my established (~3 years running) 40g that had homemade hob fuge. I used cured LR and ~4 gallons of the water from old tank to setup the Edge. I also used the gallon or so of water and a couple of the small pieces of LR that were in the fuge to help seed the sand (And not just flush my pods). Since the Edge was basically "established" I didn't have a huge cycle and the diatom issue that usually goes along with a virgin tank. I did "cycle" the tank but wasn't much, but I also wanted to check everything out for function.
The issue I ran into after "cycling" and making sure everything was stable. Was after adding small cleanup crew and transferring my two maroon gold band clowns and their small BTA from old tank. I noticed low Ph 7.6-7.8 and an acceptable dkh of ~11-12, but didn't really have any headroom to go higher on dkh. So the average buffers were not really an option as i didnt want dkh any higher. Let me say this upfront, I have and will dose if I have to BUT, I am a firm believer in finding the root cause of something as opposed to just dosing. As a rule if I do dose it is only to replace what is being used by corals (mainly Ca&Iodine and Mag if required for proper Ca/Mag ratio). I do also use PurpleUp because of the iodine included in it In my opinion the absolute best "dosing" is regular water changes (Especially in a tank this small).
All that being said, after thinking of what would be causing my low Ph it occurred to me that with the small opening on the sealed top of Edges, I did not think I was getting a decent gas exchange because of the reduced water to air surface area. I suspected CO2 could be high and the whole carbonic acid deal was going on. I'm sure there are threads discussing the CO2 issue but in a nutshell CO2 reacts with organics/water to form H2CO3 (Carbonic Acid). This can dramatically drop ph. (Opposite of injecting CO2 to lower ph). To try and validate this I simply installed an airstone into the tank opening running off an adjustable airpump (or you could use an inline valve to limit airflow). After 2 hours PH raised ~.1-.2 with dkh remaining unchanged. I turned the pump output down and let it run overnight so as to slowly raise PH and hopefully not shock or stress anyone. When I checked it next morning it was 8.2 and varied through tank day/night from 8.1-8.4 after that.
One thing to remember if you try this is it will make a mess from the air bubbles all coming to the surface around the opening (and it will get all over your lights-Ask Me How I Know Of course you could use something to place and hold the airstone deeper in the tank but make sure you are able to put the hood back on especially if you are not right there to monitor.
Once it was determined that CO2 was the culprit I was trying to figure out how to get the airline into the tank without being seen. When I took off the hood it occured to me if I just put the airstone inside the stock filter the water would be constantly "turned over" and air/oxygen could be distributed somewhat uniformly. With the plastic top cover in place there wouldn't be a mess (Like the first one i made) and everything would be hidden. First thought was to drill a small hole to run the airline through and silicone if needed. But what I noticed was the slot where you move the pickup tube to adjust flow. I simply ran the airline through this slot and attached the airstone underneath. There isn't as much room to adjust flow but I run it "wide open" anyway so that's not a concern. Just make sure the airstone is submersed completely in the intake reservoir. The snug fit in the filter lid holds the tubing in place and and everything is hidden as well. I would also strongly recommend a check valve be installed between the airpump and airstone. The other advantage to this is with the check valve installed you can take the airline apart and remove or change the pump without taking off the hood or pulling the top of the stock filter off. The check valve I use also has a filter in it to help keep dust from being pumped in.
A couple things to note here. While this works for me it may not work for everyone. This method will also only work if the CO2 level in the air you are pumping in is lower than the CO2 in the tank. This will work on other conventional tanks as well but with the greater surface area its not as big a problem. Hopefully this will help someone else out.