Backyard Aquaponics
A place to discuss aquaponics

The shells won't bring your pH down, Shells keep pH up but only as high as 7.6 since they usually only dissolve in liquid more acidic than that.

First off, once a system is cycled, it will tend to drop in pH so starting a system with water that is around 8 or a little above is ok. As the system cycles, the pH should drop unless your growbed media is something like marble or limestone which may buffer the pH up to 8 or above.

If you have shells, limestone, marble or other strongly alkali growbed media, you will not be able to bring the pH down and keep it down with acid unless you put in so much acid that you dissolve away all the growbed media.

If your system has not cycled (I'm assuming we are talking an aquaponic system and not straight Hydroponics) get past the cycling before you start trying to adjust the pH, there may be no need for adjusting once the system is cycled. Actually, once the system is cycled, you will probably need to get some shell grit from the feed store (like what you give to laying hens as a calcium supplement) to buffer the system to keep the pH up.

A pH close to 7 is what most people think of as ideal though some people run lower than that and many of us run higher (7.6) because that is what the shells buffer to.

If you are talking about straight hydroponics, you will probably need to order a nutrient mix that is formulated for hard water since constantly adding acid is usually not very effective with hard water.

This is what I was trying to say, but left out the bit
"Based on the premise, that like my media, it's the clay fines that came with the media that are doing the buffering"
So yeah I was advocating adding enough to completely remove the offending substance.

as for what to do, as TC says, cycle your system and then see. if need be replace gravel with an inert type. Eveything should come good in the end, these systems have a habit of finding equilibrium on their own.

The wood I used may have been elm; it was old and all the bark was gone.
You'd have to experiment with getting the right amount in your fish tank.

If you find a nice section limb or piece of driftwood, you can wash it off with water from the fish tank. The tannins bring down Ph in a slower, stabler, more controlled fashion. Yep, the water gets darker, and some fish prefer that. Since aquarium people have been doing this for years--and many of them have more invested in fish than the average AP person, it might be your best temporary bet. But I'm a novice at this so do your own DD (due diligence).

If you dont want to increase pH do not add Mangrove Root. These will definitely increase pH due to the very nature of the plant stock [semi submerged in saltwater] I know of fish folk who have done so and have had to completely rebalance their system to get the levels back to suitable, I guess the same as shell grit hey?

Good to know ...... now to find some old elm

After recent issues with high pH, think I may try some driftwood in my system. The tap water and growbeds are all limestone so it should be good, right? How much driftwood should I add to my 10 gallon (pH now is 7.6+)? I'm mainly trying to get it down so the sprouts can grow. I'm tired of looking at my two month old sprouts.

I have no idea what kinds of wood will work and what wont. However, you will see cautions in this thread against cypress and resinous woods. My 500 gallon fish tank (not yet in use as a fish tank) has a Ph of 8.4 or higher, possibly due to a lot of organic matter. I'm going to look through the firewood pile for stuff without bark, throw it in and see what happens.

Can't say how much to use either. Let's experiment and compare notes.

Oops, in the entry above, I was getting the water's high ammonia confused with Ph. Organic matter can cause high ammonia. Not sure why the Ph is so high. Just tested a bucket of tap water sitting for a week so in order to evaporate chlorine; it has a Ph of 7.4 or so.

A week are they poisoning the water on your side of the world

Speaking of tannins. Would grapes have the same effect as wood?

I'm currently trying large pieces of coral but I think I'll be switching to something smaller, liked crushed coral.
Also will be putting it in a more direct flow area.

Has anybody ever tried plaster of paris? I've read articles about how they cut the bottom of 5 gallon buckets and mixed batches of plaster of paris to form large pellets. Supposed to be safe and able to just drop it in and replace as needed.