red -vs- black cinder as grow medium

[opihiman911]

I live on the small island of Kauai, Hawaii and we have very limited selection of hardware and other aquaponic supplies. Heck, almost noone here on my little island even knows what aquaponics is.
Readily available on island I have a choice of drainage gravel from local quarry (not sure what kind of rock it is), red, & black cinders. They all cost the same, so pretty much settled on using cinder becasue of the weight issue with gravel and I don't know what the gravel will leach.
Which cinder is better? When I was looking at the black cinder it looked pretty small, maybe large lima bean sized, as compared to the red cinder whick was a larger cherry tomato sized. I found several opened black cinders and they all seemed small sized.
I read a post somewhere about one cinder raises the ph and the other one lowers it, but can't find that info again.
I was leaning toward the red cinder because 1) the size of the cinders and 2) I live in a hot dry area and am concerned about the black cinders heating up and holding the heat. They are both readily available and they both cost the same. What are the pro and cons of red -vs- black cinder? What about mixing the 2 50/50 blend?

Peace,
Cory

[Bidadisndat]

Cory, I'd tend to go with the larger media for ease of handling. The black may absorb more heat than the red, but not by a lot I should think. (You could always lay out a strip of each in the sun for a day then walk around on both to check. )
The cinders may be lighter to work with when they are dry, but they are also really porous and will be a lot heavier when they have absorbed all the water they can. The upside is that there is also a much larger surface area for nitrifying bacteria to grow on, and even if you have to drain the GB to work on it there will still be a lot of water retained within the rock to keep that bacteria thriving. The stuff is supposed to be Ph Neutral, but I've read that it can raise Ph slightly in aquariums, though not enough to cause a lot of concern.

Cheers,
Bid

[Ravnis]

I use the red cinder, called lava rock that I purchased from Lowe's. I have had a little bit of difficulty with ph and keeping it down. The ph tends to stay at 7.4 and everytime I try to lower it, the ph just drifts back up. Rather than stress the fish, I just let it ride there and plant growth is still good.

What I did when I was choosing this was put some in a bucket with water and some acid. Then I checked the ph 30 minutes later. I saw no change then in that small time frame. Might work for you to do the same with the red and black cinder and see what effect it has on ph soaking in water overnight.

[opihiman911]

I use the red cinder, called lava rock that I purchased from Lowe's. I have had a little bit of difficulty with ph and keeping it down. The ph tends to stay at 7.4 and everytime I try to lower it, the ph just drifts back up. Rather than stress the fish, I just let it ride there and plant growth is still good.

What I did when I was choosing this was put some in a bucket with water and some acid. Then I checked the ph 30 minutes later. I saw no change then in that small time frame. Might work for you to do the same with the red and black cinder and see what effect it has on ph soaking in water overnight.

My one person I know who has a system uses red cinder also. Interesingly she showed me that she has a bananna peel buried under her water inflow, she says it gives it gives her tomatoes and strawberries a pospherous boost to help with fruiting. I also saw what looked like a couple pieces of lemon or orange peel also buried in there. Could that peel maybe help acidify the water inflow and by the time it passes though the red cinders it help alkaline it back to neutral? From what I've learned the fish like ph 6.5-7.2 and most vegis like it 7.0-7.5 so as a comprimise you should aim for neutral ph plus or minus .2 to make both of them happy.
I'm a little reluctant to really visit this lady more often and ask her more questions. She is a really nice and polite person, but very much into organic, rock healing, crystal, spiritual, new age talk to nature kind of thing. A little to right field for me. I like unique, different, inventive kind of ideas and projects, but the need to be rooted in science or atleast on based on solid theory, not because the whales or wind told me in my dreams

Peace,
Cory

[GaryD]

Hi Cory,

I'd go with the larger one to avoid clogging with solids......(although my first preference would be to remove the solids and treat them outside of the system before returning the nutrients back into the system). Mixing them may not be much use because you'll end up with a similar air void as if you used all small ones.

.......and most vegis like it 7.0-7.5

Most vegetables operate in the range of pH 6. - 7.0 (see here)......and the closer to pH 6.0 that you get, the more available several key nutrients become and the less you'll have to supplement your system with things like iron, potassium and calcium. For a better understanding of the relationship between pH and nutrient availability.....see here.

Gary

[opihiman911]

Hi Cory,

Most vegetables operate in the range of pH 6. - 7.0 (see here)......and the closer to pH 6.0 that you get, the more available several key nutrients become and the less you'll have to supplement your system with things like iron, potassium and calcium. For a better understanding of the relationship between pH and nutrient availability.....see here.

Gary

Gary,
Thanks for those links. When I compared that ph/nutrient availability chart to my one I have for an organic soil fertilizer, the whole chart is shifted to the right one bar (.5 more alkaline)
I just assumed soil ph and water ph for plants would be the same. In my organic soil garden I aimed for 6.5- 7 neutral and always had to add lime because my soild would drift down to below 6.5 after a couple seasons. From what I understood, the good soil bacteria is more active at converting organic material into usable nutrients when it was closer to neutral. Below 6.5 and the bacteria would die from the acidity and nutrients available to the plant would slow down.
I guess that is similar to water based as the system becomes more acidic the nitrifying bacteria slow down, but since there is a constant supply of ammonia from the fish, the plant always have a nutrient supply.....if I understand right.
Just curious where do you keep you water ph at? what range would you keep it at without making any intervention with an emphesis on vegi production and not really mattering if or when the fish get to eating size.
Still on a steep learning curve.

Peace,
Cory

[GaryD]

Hi Cory,

From what I understood, the good soil bacteria is more active at converting organic material into usable nutrients when it was closer to neutral.

Nitrifying bacteria grow most effectively at pH 7.5+.

Below 6.5 and the bacteria would die from the acidity and nutrients available to the plant would slow down.

There will still be plenty of nitrifying bacteria around at pH 6.5 and nutrient availability at pH 6.5 will be greater than at higher pH.

I guess that is similar to water based as the system becomes more acidic the nitrifying bacteria slow down, but since there is a constant supply of ammonia from the fish, the plant always have a nutrient supply.....if I understand right.

Nitrifying bacteria exist in the millions in even a small AP system. Even if you cut their numbers by 50% there are still plenty around to convert the ammonia.

Just curious where do you keep you water ph at? what range would you keep it at without making any intervention with an emphesis on vegi production and not really mattering if or when the fish get to eating size.

My system is currently around pH 6.7. The system has pretty much matured so it doesn't move around too much. Right now, temperature is much more an issue in my system than pH.....because I grow warmwater species like barramundi and jade perch.

At the moment, we have excellent plant growth.

Still on a steep learning curve.

You and everyone else......but stick with it. It gets easier.

Gary