I am sure you mean "ph controller", not "co2 controller" . Low KH means small amount of CO2 can produce large ph change. In a sense, the controller is even more useful here to make sure you do not have a ph crash. The accuracy of your ph controller is not dependent on your kh, it depends on the resolution/calibration of its ph probe. However, you are better off increasing KH to 3-4 degrees so that you have sufficient CO2 for plant growth.
It'll work better at lower light(using low KH's) since there is less CO2 demand and less potential for the plants/bacteria using up the KH for a carbon source.
But in theory, I think a KH of 1-2 if fine.
Keeping it there(the KH) might mess with you depending on your routine and system.
A KH of 2 is generally fine.
Do not rely entirely on the pH controller to take care of all things CO2 for you, you will need to keep a close eye on the KH, you wanted to keep the KH at a low narrow range, so that's your new job, I do weekly large water changes and have a slightly higher KH and then I never have to worry. Even if you are breeding Apisto's, I really do not think you need to go this low. They have done well at 2KH and unless you are breeding wild stock, I see no reason to go this low.
Work of the diet more, less on the KH.
My reason for running with such a low KH is because I would like to experiment with Tonina and Tonina type plants. I have tried to grow these at KH of 7 before and I have had no luck. They would hang on for about a month and a half but always would eventually die. So I figured I would give the lower KH a try and see what comes of it. These are some of my favorite plants and I would like to be able to grow them.
I am running with very high light and have not seen any problems as far as CO2 is concerned. I am using a Reactor 1000 on a 30 gallon tank so the CO2 does disolve very rapidly. I will keep a close eye on the KH as you suggested Tom.
I have tried Tonina in harder water KH 7 GH 3-5 on three different occasions with not much luck. All other plants were growing just fine.
At the time I was growing plants like Stargrass, Pearlweed, Eriocaulon's, Ludwigia cuba, HC, Downoi, R. macrandra, but I just couldn't keep the Toninas alive. The Tonina would hang on for about a month to a month and a half and then just start turning brown and waste away to nothing.
Maybe you can tell if you see something wrong with my fert regime.
30 gallon, 3.6wpg PC, 10ppm KNO3, .73ppm PO4 every other day and on the other days I add 7.5ml of Flourish and 5ml of Flourish iron. 50% water change on Saturdays. CO2 kept at 30ppm with a controller.
Like I said everything else grew just fine and is still growing just fine.
I have grown Egeria najas in the past but didn't like the intense growth.
Like I said though this is basically an experiment. I have been hearing you in the past putting down the need for soft water with some plants and I thought since the harder water wasn't working so good for me I would see what happened with the soft water. Believe me I tried my best to put this "myth" to rest myself and just couldn't. Now I want to see what will happen with the soft water.
My tonina was growing well in KH4 GH6, however it quickly died when I ran the tank without ferts in the water column for a month. It was the only one to do so, all other plants didn't mind the absence of ferts for that period and only showed small problems. The tonina became brown very quickly and never recovered, seemed to ignore the fact that it had a lot of nutrients available in the substrate too...
I keep the nutrients higher than the other plants "need" as well.
I dose more NO3, about 11ppm every other day and about 1.5x more trace.
I used no substrate fertilization (aged Flourite), very few fish, low bioload etc. are coming from as far as a problem plant and the soft water issue. Everytime I've re evaluated this, I've burned myself and proved myself wrong.
I've honestly felt the same and searched for differences, I cannot find them, I am always vigilent for that one soft water only plant, if it does exist, but that holy grail has yet to have been found by me.
In order for something to be true, such as PO4 causes algae, you must show that in controlled conditions that PO4 dosing causes algae.
If not, the algae must be being caused by something OTHER than PO4, this is no different.
I've already stated I've grown it at a KH/GH combo higher than many say.
So I already know it works.
The CO2 was very high, light, nutrients etc.
I will not rule out some help from the substrate, this plant did produce a fairly strong root system. Being a SA plant, it is very likely amphibious and from the natural pics I've seen, is found in shallow faster flowing water.
A frozen peat ball might help.
I did not try that, I had no issues with the plant although many folks seem to and most everyone seems to believe that soft water will cure their issue.
I highly doubt it, at least as it being the cause of the growth problem.
I've grown two species of Tonina and Eriocaulon setaceum at Kh/GH 4/5 in Miami. It even grew, albeit slowly, with no CO2 and only 2 wpg. They grew well, although much better in the higher lighting and CO2 enriched conditions. I consider Miami's tapwater to be soft.
It didn't work out too well in KH/Gh 11/13, Chicago's water, though. The plant grew fine for a couple weeks before turning a transparent brown color. I consider Chicago's tapwater to be pretty hard. It's even harder in the winter.
A KH of 2 is fine for all practical purposes.
I and other's suggest 3 mainly as a large margine of error, but 2 or 1 will work if you want.
My issue is that it's not the KH, KH is not a nutrient unless it's reduced to CO2=>sugar.
Therefore harder water will have a more stable eniroment and also have more Carbon should the CO2 run low.
This is why you find better plant growth is harder waters=> more nutrients.
Plants that live in spartan environments live not because they like it, they are there because they are poor competitors elsewhere.
Many plants fall into this same situation and have similar traits. This is not just an aquatic issue.
Tonia is fairly slow growing vs Egeria najas which is very fast, but Tonia has a special niche that allows it to grow slow, but better in nutrient poor environments. It has a better root development and one could argue is therefore better adapted to poor water column conditions than Egeria.
But it does not mean it perfers it!
Non CO2 methods changes the rate, Proserpinaca grows wonderful in non CO2 systems with softer water as well, but doe sgreat in CO2 hard water systems too.
It's a nice plant, but it's not the cat's meow IMO.
Hey, you have 300 other species to grow, come back later and try it out again. I told you what I did.
Eriocaulon is a very beautiful plant. It does well and so did everything I tried out in that same tank, I had to give away buckets of B japonica, Red Cabomba, hairgrass etc.
Folks said these were all soft water plants also way back when. It's a fall back if someone cannot explain something, no one has shown me why there is a basis for it in terms of plant growth and I have yet to have found anything other than some observations/speculations, my own included over the years.
Often said, but never proved. Well, I guess I'll get to it at some point.
The research done to date suggest harder, no softer water produces better growth in several common aquatic sumbersed plants(Pondweed, Milfoil, Hydrilla).