I have been looking for a Hydroton replacement for a while now. As my my small system is inside on a wooden floor, gravel or river rock is too heavy. My local greenhouse supplier gave me a call last week about a product called Gold Label Hydrocorn. A single hydroponic substrate. This is supposed to be a Hydroton replacement so I thought what the heck, and bought a 45L bag. Its about the same price as Hydroton. The media is expanded clay, although not as uniform in size or shape as Hydroton. It is, for the lack of a better word, quite "lumpy" in appearance, which to my mind is a plus because of the greater surface area exposed to the fish water. I used it to top off a 40gal grow bed,and in 3" net pots in the 2*4 DWR. Herbs and spinach in it. Everything sprouted, the fish are still happy, and the water quality has not changed one iota.
I don't know if the product is available everywhere, but here is the website:
For metal analysis: http://www.aafp.org/metals.htm
Maybe this will be of use to someone in the community
Roger, there are a lot of questions that don't have direct answers, and most anything involving pH is one of those topics. Why 6.2? Because the plants, most plants, want and need a low pH. It would be better to have a pH of 5.2 than 6.2, for the availability of nutrients, but we are limited to the realm above 5.5 for the sake of the bacteria. In soil, there exists micro-pockets of various pH ranges, depending on the bacteria, minerals, and "foods" present. This soil pH diversity makes soil much less of a concern to regulate pH, because the plant roots can locate optimum zones for what it needs. However, in water things are much more homogenized, and it is really a fairly narrow range of suitable pH for great plant production, especially those plants that pull the heavy nutrients. Lettuce can grow in tap water, and so can strawberries. In like reasoning, carnivorous plants want extremely soft water, like rain water or distilled water. They get their minerals from bugs, not soil, and this adaptation lets them grow in swamps where other plants can not. I run my systems now at 6.0 to 6.4, and if I'm lucky, it stays in this range with no extra inputs. Nitrification pulls it down to 6.0, and hard water lifts it to 6.4, if I had an auto-fill hooked up (soon), then I would guess I would hover at 6.2 Why walk the tight rope? Well, I suppose I agree with Vlad, I don't consider the chore a headache. I used to not care what my pH was, and was quite lucky for the first year. I never checked it, and everything grew great. But as the water passed it's one year birthday old my pH rose until it glued to 8.3
Why 8.3? Funny you should ask, and I wondered too. When I first realized it was high pH that was causing my poor plant growth and deficiencies, I started adding acid, and next day it was back to 8.3. This happened dozens of times, even when I'd get pissed and dump way too much acid. I once dropped it instantly from 8.3 to 4.5, not smart. The tilapia didn't seem to notice, but the pangasius thought it was nuclear holocaust. Next day, back to 8.3
Which brings us to your alkaline media. If you could find a blend of minerals that held a pH of 7.5, and your top up water was pretty neutral, then you might have a great time. The trouble is that most hardness is caused by CaCO3, and CaCO3 has a pH of 8.3. It will forever attempt to raise the pH to 8.3, and will do so until enough acid is added to dissolve it all. If pH rises above 8.3 somehow, then the CaCO3 will precipitate out as solid (limestone), where it will hang out forever until pH lowers and dissolves it again. That is one reason that CaCO3 is a good, safe buffer, because it cannot raise above 8.3. CaOH on the other hand, can nuke your pH to the moon.
So, can you add Ca and Mg without increasing pH? Yes, by using divalent ion salts (Fe, Ca, Mg) which do affect GH, but not KH or pH. And by adding fish food that contains a good blend of minerals including Ca and Mg, which is much more simple. If you start with good water, and keep your pH in the low 6's, and feed your fish plenty of healthy, diverse foods, you shouldn't have a deficiency. IMO. Oh yeah, one more thing. Fish do fine at a pH of 6.0 as long as it is stable and the water has decent hardness.
...What Jon said
I guess to that wonderful explanation I'll just add that our divalent cations are pretty much all base metals...being base metals, they dissolve and/or dissociate from complexes into their natural oxidation state (which is +2) much better in an acidic environment. This +2 state happens to be the 'plant available form' of such elements. This is a big reason why plants do better at lower pH ranges (5 to say 6.5) than at higher ones. Also, base metal cations, at higher pH ranges (above neutral) will want to form complexes with other things floating around in the AP water...Like phosphates or carbonates...Here's an example. CaCO3 at an acidic pH will dissociate to plant usable Ca2+ and some CO2 gas...a good thing right? But as should the pH rise, it (the Ca2+) will form complexes and precipitate out of solution (not good, and not plant available...bad).
These complexes most often come in the form of phosphate or carbonate complexes. That same Ca2+ will form a whitish grey precipitate called calcium phosphate (CaPO4). (This is just one of many such complexes that may form). And it's not just calcium, but iron, magnesium, zinc, potassium...again pretty much all of the divalent base metals will do this to a greater or lesser degree. The lower the pH, the more of those elements that will be in solution (dissolved in a +2 state and hence plant usable) instead of floating around in a 'big' clunky complex molecule that a plant cannot absorb/use.
Thanks so much for the info! I just posted a question 2 days ago asking if anyone had heard of this very product! I was considering using it in my indoor media bed (also on a wooden floor), and was hopeful because I wanted use it instead of the (heavier) river rock. Great to hear you've had success with it. Would you recommend using this on top of something else? I was just thinking of just filling my media bed with this material alone.