Having read through this thread, I may be able to clear up a few misconceptions. Because I believe it is always better to see the full picture I will repeat some things already said.
First, aquatic plants need sufficient light intensity to drive photosynthesis, and they need sufficient nutrients in balance. The "balance" aspect is crucial. Too much light, or too little, or too many nutrients, or too few, and plants cannot photosynthesize sufficiently (or at all, depending) and algae will become problematical.
Nutrients are 17 in number. There are macro nutrients (more of these is needed) and micro nutrients (less).
GH is general hardness, which involves minerals but primarily only two of them, calcium and magnesium. Other minerals can contribute to the GH but normally, especially in tap water where laws regulate the levels of heavy metals and such, it is calcium and magnesium. So GH alone is not going to tell you if all necessary nutrients are present. The other thing to keep in mind always, if fish are to be kept in the aquarium with plants, is that plants are much more adaptable than fish when it comes to GH, KH and pH. We can easily supplement minerals for plants but if the GH is wrong for the fish species the fish will have serious issues. Fish first.
I have source (tap) water with a GH and KH almost zero. I keep fish that need this. I have plants in all my tanks, and I use substrate fertilizer tabs for some, and liquid fertilizer for others, primarily. The liquid obviously benefits all plants.
With a GH around 3 to 4 dGH, you are ideally situated for most plants. Stay with soft water fish.
Now, the GH as I said above is primarily calcium and magnesium. You may have to add the other nutrients, depending upon the plant species; different species have different needs for light and nutrients. Fish foods contain all nutrients the plants can use (from fish excrement in the substrate as it is broken down by bacteria) but again depending upon species these may or may not be sufficient alone.
Iron was mentioned. It is generally not safe to add individual minerals like iron, unless you know the proportion of all of them. It is a fact that aquatic plants require their 17 nutrients in a rough proportion to each other; too much of some of them can cause plants to shut down assimilation of other nutrients. So it is important to not overdose any one nutrient. Red leaf plants need more light intensity than green leaf plants, and this is usually where red plants fail. The colour of plant leaves is due to the light being reflected, so red leaf plants are reflecting red light. But red light is also crucial for photosynthesis, along with blue, but red is the more important of the two. So, red plants will need brighter lighting than green plants, generally. [There are always exceptions.]
The pH is generally unimportant to plants, though again not to fish. Most aquarium plants come from regions with very soft water (zero GH and KH) and generally an acidic pH (it can range from the 3's up to the 6's, but it is on the acidic side (below 7) in most places. There are exceptions. Some plants, like Vallisneria, occur in waters with higher mineral content; they even occur in the African rift lakes which is the hardest and most basic (above 7) pH of any fish we keep. These plants can use bicarbonates, which brings me to the carbon (CO2) issue.
Carbon was mentioned. Plants prefer this as CO2. Some can only use CO2, others (like the Vallisneria) can also use bicarbonates. But CO2 will be used by all plants regardless. Natural CO2 occurs from the normal continual respiration of fish and plants and some bacteria species. But there is much more produced by the breakdown of organics, which is primarily in the substrate. This is often much more than many people realize. Before jumping into thinking you need diffused CO2, you need to asses your light, intended plant species, and fish. The more fish and the more you feed them, the higher the organics and thus more CO2. With many plants this is adequate. Lighting as I said at the beginning drives photosynthesis, so it has to be sufficient for the plant species and balanced with the CO2 and other nutrients.
I personally don't recommend soil substrates. But to answer a couple questions...yes, a soil substrate will increase the CO2 because it contains organics that get broken down by bacteria. This also produces ammonia...any decomposition of organic matter produces ammonia and CO2. Fish also respirate both. So having soil can indeed increase ammonia, and during the first six months or so, it is very possible to literally poison fish with excess ammonia.
I can expand on the above if asked.
Byron.
First, aquatic plants need sufficient light intensity to drive photosynthesis, and they need sufficient nutrients in balance. The "balance" aspect is crucial. Too much light, or too little, or too many nutrients, or too few, and plants cannot photosynthesize sufficiently (or at all, depending) and algae will become problematical.
Nutrients are 17 in number. There are macro nutrients (more of these is needed) and micro nutrients (less).
GH is general hardness, which involves minerals but primarily only two of them, calcium and magnesium. Other minerals can contribute to the GH but normally, especially in tap water where laws regulate the levels of heavy metals and such, it is calcium and magnesium. So GH alone is not going to tell you if all necessary nutrients are present. The other thing to keep in mind always, if fish are to be kept in the aquarium with plants, is that plants are much more adaptable than fish when it comes to GH, KH and pH. We can easily supplement minerals for plants but if the GH is wrong for the fish species the fish will have serious issues. Fish first.
I have source (tap) water with a GH and KH almost zero. I keep fish that need this. I have plants in all my tanks, and I use substrate fertilizer tabs for some, and liquid fertilizer for others, primarily. The liquid obviously benefits all plants.
With a GH around 3 to 4 dGH, you are ideally situated for most plants. Stay with soft water fish.
Now, the GH as I said above is primarily calcium and magnesium. You may have to add the other nutrients, depending upon the plant species; different species have different needs for light and nutrients. Fish foods contain all nutrients the plants can use (from fish excrement in the substrate as it is broken down by bacteria) but again depending upon species these may or may not be sufficient alone.
Iron was mentioned. It is generally not safe to add individual minerals like iron, unless you know the proportion of all of them. It is a fact that aquatic plants require their 17 nutrients in a rough proportion to each other; too much of some of them can cause plants to shut down assimilation of other nutrients. So it is important to not overdose any one nutrient. Red leaf plants need more light intensity than green leaf plants, and this is usually where red plants fail. The colour of plant leaves is due to the light being reflected, so red leaf plants are reflecting red light. But red light is also crucial for photosynthesis, along with blue, but red is the more important of the two. So, red plants will need brighter lighting than green plants, generally. [There are always exceptions.]
The pH is generally unimportant to plants, though again not to fish. Most aquarium plants come from regions with very soft water (zero GH and KH) and generally an acidic pH (it can range from the 3's up to the 6's, but it is on the acidic side (below 7) in most places. There are exceptions. Some plants, like Vallisneria, occur in waters with higher mineral content; they even occur in the African rift lakes which is the hardest and most basic (above 7) pH of any fish we keep. These plants can use bicarbonates, which brings me to the carbon (CO2) issue.
Carbon was mentioned. Plants prefer this as CO2. Some can only use CO2, others (like the Vallisneria) can also use bicarbonates. But CO2 will be used by all plants regardless. Natural CO2 occurs from the normal continual respiration of fish and plants and some bacteria species. But there is much more produced by the breakdown of organics, which is primarily in the substrate. This is often much more than many people realize. Before jumping into thinking you need diffused CO2, you need to asses your light, intended plant species, and fish. The more fish and the more you feed them, the higher the organics and thus more CO2. With many plants this is adequate. Lighting as I said at the beginning drives photosynthesis, so it has to be sufficient for the plant species and balanced with the CO2 and other nutrients.
I personally don't recommend soil substrates. But to answer a couple questions...yes, a soil substrate will increase the CO2 because it contains organics that get broken down by bacteria. This also produces ammonia...any decomposition of organic matter produces ammonia and CO2. Fish also respirate both. So having soil can indeed increase ammonia, and during the first six months or so, it is very possible to literally poison fish with excess ammonia.
I can expand on the above if asked.
Byron.
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