RupertofOZ wrote:
Others use Muriate of Potash (Potassium Chloride)... again, continual usage may increase salinity... it's also used as a means of execution, as it stops the heart... for this reason I'm somewhat wary of it...
Potassium Chloride is no more toxic than Sodium Chloride, At similar dosage, both can stop the heart. It is all in the dosage.
However that said, I don't think there are any materials that are completely safe to add into a system without some caution. Even water added too much can cause your system to overflow if you know what I mean.
Anyway, back to pH and buffering. Systems tending to go acid is really common. You don't really want to be adjusting your pH all the time though since bouncing the pH around is hard on all living things involved (fish, plants, and bacteria as well as the person constantly having to adjust and test.) Once you have the pH adjusted where you want it, you want to make sure your system has adequate buffering. How much seashells? My system is completely full of them as they are more than 1/3 rd of my grow bed media. My system has never seen a pH below 7.5. My situation is a little overkill but since my top up water is well water that has a normal pH around 8, at least having my system buffered to the hilt keeps me from bouncing the pH too much if heavy top ups or water changes are needed.
Buffering materials
Shell Grit like sold for chickens as a grit and calcium supplement is usually easily gotten and already ground to make more surface area available for buffering. You want your buffering materials placed where water has to flow through them. Simply placing a bag of them in the fish tank might not really get the acidic water filtered through them enough to really buffer your whole system. Some people place a basket or something with the shells at the inlets to grow beds or where water enters the fish tank so the water has to flow through it to get where it's going.
So......
Shells
Shell grit
Limestone
Marble
those are all materials that will dissolve and buffer pH, the limestone and marble might tend to buffer too high so use carefully.
On the other side of things, adjusting pH down. Vinegar, lemon juice, acid etc might work to adjust the pH down but in my experience, it is usually not going to be a good thing to do. Problem is, vinegar and lemon juice are organic and quick to break down so the effects are usually short and simply result in bouncing the pH. More important would be to figure out why the pH is so high.
Usual 3 reasons...
1-hard well water
2-media
3-algae
If hard water is the reason, then once the system is cycled, the pH is likely to drop and needs buffering anyway so don't panic. (Be aware that water right out of the tap is likely to show a lower pH than the true pH of the water so let the water air out before testing the pH.)
Sometimes people use gravel that has a strong effect on the pH of their system. Limestone or Marble are two common examples of media that can cause high pH. If this is the problem, adjusting the pH with acids will only waste your time and dissolve your media slowly.
If Algae is the reason the pH is low or high (algae can cause pH to be really low in the early morning due to a lack of O2 in the water and an abundance of CO2 while come late afternoon it will have used up the CO2 and be producing O2 causing the pH to be high) rather than trying to adjust pH that is doing weird things due to algae, one is better off shading the tank and where ever else lots of water is in the sun.
Backyard Aquaponics
I know, I know,