A few issues from the last posts here, now that we know the numbers.
With a GH of 11 and a KH of 6, no amount of wood or organics will lower the pH below 7. That is just not possible. Assuming the water people are not adding something to increase it, the pH will not likely lower at all. If there is something raising it, beyond the inherent GH and KH, it might come down. But not below 7 unless you dilute the water GH/KH by adding "pure" water.
Second and related issue...do not use pH adjusting chemicals ever if fish are in the tank. These will not work to begin with, because as soon as you lower the pH with one of these solutions, the GH/KH will raise it back, and the fluctuating pH is far more serious on fish, even deadly. The store people who recommended this clearly have no idea of chemistry in a fish tank, nor fish physiology. And I would tell them that to their face if given the opportunity.
It is the GH that matters most, because this involves the level of calcium and magnesium in the water, and if one understands the physiology of freshwater fish it becomes obvious that the effect of these minerals is far more significant. Hard water fish species must have these minerals in the tank water or they cannot function properly, and they will slowly weaken and if they do not succumb to some issue along the way (which with the correct water hardness they would easily be able to deal with), they will have an early demise. Soft water fish have similar problems but the opposite. Kept in hard water, the calcium especially is pulled out of the water entering the fish (which is continual, via osmosis through every cell) by the kidneys, and an early death is due to calcium blockage. The pH is not as critical, within reason, and provided it remains relatively stable; fish must adjust their blood pH to equal that of the water they live in, so every change beyond the normal diurnal fluctuations takes more energy to deal with, and there is a limit.
Last issue, the fish species mentioned. Celebes Rainbowfish are fine, as you realize. Zebra danios will have no issues here; they are technically a soft water species, but they have a decent tolerance and provided things remain stable will be OK. As for Pearl Gourami, the GH and pH are not what they would be happiest with, from a functioning viewpoint, but as you already have them, stay the course.
I will end with a general comment. Seachem and API are both trusted names in this hobby, and for good reason. But, the fact remains that not all of their products are advisable. They may say "x" product is "safe" for fish, but this is not technically accurate some of the time. The fact that using "x" does not cause the fish to turn belly-up within minutes does not mean it is "safe" long-term. Some of the products are not "safe," period. I used to use Equilibrium, a plant additive that increases certain minerals to raise the GH [I have zero GH/KH water out of the tap]. I stopped using this after I was having a disease issue and getting help and advice from a marine biologist. She asked me point blank just what good I thought this products was doing to my very soft water fish, and the question got me thinking. Every substance we add to the water in an aquarium, from conditioner to plant additives to "medications" and such, has the likelihood of entering the fish's bloodstream and internal organs, if the substance is molecularly capable of diffusing across the cell membranes. None of our fish species have evolved to function with these chemicals, so the fewer we use the better. And many are downright dangerous and will lead to fish death in time.
With a GH of 11 and a KH of 6, no amount of wood or organics will lower the pH below 7. That is just not possible. Assuming the water people are not adding something to increase it, the pH will not likely lower at all. If there is something raising it, beyond the inherent GH and KH, it might come down. But not below 7 unless you dilute the water GH/KH by adding "pure" water.
Second and related issue...do not use pH adjusting chemicals ever if fish are in the tank. These will not work to begin with, because as soon as you lower the pH with one of these solutions, the GH/KH will raise it back, and the fluctuating pH is far more serious on fish, even deadly. The store people who recommended this clearly have no idea of chemistry in a fish tank, nor fish physiology. And I would tell them that to their face if given the opportunity.
It is the GH that matters most, because this involves the level of calcium and magnesium in the water, and if one understands the physiology of freshwater fish it becomes obvious that the effect of these minerals is far more significant. Hard water fish species must have these minerals in the tank water or they cannot function properly, and they will slowly weaken and if they do not succumb to some issue along the way (which with the correct water hardness they would easily be able to deal with), they will have an early demise. Soft water fish have similar problems but the opposite. Kept in hard water, the calcium especially is pulled out of the water entering the fish (which is continual, via osmosis through every cell) by the kidneys, and an early death is due to calcium blockage. The pH is not as critical, within reason, and provided it remains relatively stable; fish must adjust their blood pH to equal that of the water they live in, so every change beyond the normal diurnal fluctuations takes more energy to deal with, and there is a limit.
Last issue, the fish species mentioned. Celebes Rainbowfish are fine, as you realize. Zebra danios will have no issues here; they are technically a soft water species, but they have a decent tolerance and provided things remain stable will be OK. As for Pearl Gourami, the GH and pH are not what they would be happiest with, from a functioning viewpoint, but as you already have them, stay the course.
I will end with a general comment. Seachem and API are both trusted names in this hobby, and for good reason. But, the fact remains that not all of their products are advisable. They may say "x" product is "safe" for fish, but this is not technically accurate some of the time. The fact that using "x" does not cause the fish to turn belly-up within minutes does not mean it is "safe" long-term. Some of the products are not "safe," period. I used to use Equilibrium, a plant additive that increases certain minerals to raise the GH [I have zero GH/KH water out of the tap]. I stopped using this after I was having a disease issue and getting help and advice from a marine biologist. She asked me point blank just what good I thought this products was doing to my very soft water fish, and the question got me thinking. Every substance we add to the water in an aquarium, from conditioner to plant additives to "medications" and such, has the likelihood of entering the fish's bloodstream and internal organs, if the substance is molecularly capable of diffusing across the cell membranes. None of our fish species have evolved to function with these chemicals, so the fewer we use the better. And many are downright dangerous and will lead to fish death in time.
As for RO water (the original title of this thread), I may go down this path at some later point. But for the sake of this thread, I feel satisfied and complete (well, for now - LoL) Thanks everyone for your time.
