PH Low

Not new to aquariums, been in the great hobby since late 70’s. Had fresh and salt over the years but been away for a while. Six months ago, got the itch again, bought a small 10 gallon set up after a few years of bettas, new tank, led hood, hob filter, heater, etc… Tank has been doing fine, do water changes, clean up, all the normal stuff. Also check water with API Master test kit, a lot less to mess with than years ago with large salt tanks. Anyway, first test, Ph was to me low, 6.8 but no issue. Did a test yesterday and was around 6.0. I’ve been testing every week or so and seems like PH is dropping. Also tested tap water and came back at 7.5 but did not let it sit 24 hours. What would cause tank water to lower PH readings. All other readings are excellent fish are fine. And yes, besides the Master kit, I do have an API PH kit, bot came back with same reading the other day.

This is very natural, so natural as to be normal. But to understand it, you/we need to know the GH (general hardness) and KH (carbonate hardness or Alkalinity) of the water. Rather than buying a test, check the website of your water authority and it may (should) be there.

The three parameters, GH, KH and pH are closely cponnected. You cannot safely or effectively adjust the pH without knowing the GH and KH, and possibly (depending upon these values) adjusting those too. I will explain more when I have the numbers. By the way, when testing tap water (you need to know this on its own), out-gassing the CO2 is necessary or the reading may be lower that it actualy is. CO2 creates carbonic acid which obviously lowers the pH, but when the CO2 dissipates out the pH will return to "normal."

Another point, there is no problem with lowering pH provided you maintain soft and very soft water fish species, since most come from such water. The Rio Negro, the world's largest blackwater river and the third largest tributary of the Amazon has a pH in the 4 range and hundreds of species thrive. However, if you keep fish from harder and basic water, such as livebearers, this will cause issues. I'll leave that until I know the fish, and the GH/KH/pH of the tap water. [I can see some species in the photos, but let's have the species and numbers.]

Thanks Bryon, nothing special, 2 Rasboras, 3 Guppies, 4 Neon Tetras, 2 Platys. A little over stocked for a 10 gallon, but water, health seems fine, all active, got one small hunk of Java moss growing. To me it was just weird with the low PH. I’m not one to add things to adjust, I believe in cycling, cleaning, water changes. It was just a question on the low PH… This site is great by the way for info! Let me know, thanks!!!

Ed Pursell said:

Thanks Bryon, nothing special, 2 Rasboras, 3 Guppies, 4 Neon Tetras, 2 Platys. A little over stocked for a 10 gallon, but water, health seems fine, all active, got one small hunk of Java moss growing. To me it was just weird with the low PH. I’m not one to add things to adjust, I believe in cycling, cleaning, water changes. It was just a question on the low PH… This site is great by the way for info! Let me know, thanks!!!

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What I can tell you is that long-term the platies especially and probably the guppies too will have internal issues and slowly weaken and die. We really need to know the GH especially, because this is critical to these fish. The lowering pH suggests without question that the GH and KH are most likely low, i.e., "soft" water, so this is something you need to know and then deal with however you decide.

The issue is the dissolved calcium and magnesium in the water. Fish from naturally harder water have evolved to function in such water, and when placed in differing water parameters will weaken which makes them more susceptible to other problems that normally they would easily handle. The GH is the crucial parameter, followed closely by the pH.

However, the soft water fish (tetras, rasboras) are in their element with an acidic pH, and if my assumption on the GH being low is correct this too is perfect for these fish. There is no middle road, depending upon the numbers. Increasing the GH/KH/pH would benefit the platies, but at the expense of weakening the rasboras and tetras, again depending upon the numbers.

Based on the location listed for you I found this 2021 water quality report. I cannot be entirely sure it is the correct one but based on this 30ppm KH and 28ppm Gh plus 18ppm Chloride and 20ppmm sulfate. These numbers are not unusual for tap water. Some of the chloride and sulfates are probably in the form of salcium and magnesium sulfate and chloride.

Based n the photos Some of the plants appear artificial and you have a bit of moss in the water. Lifving plants need calcium, magnesium, chlorine nd sulfur to grow. IAnd if your plant are growing they will consume mostly calcium and magnesium but only a small amount of the chloride and sulfur. So as the water ages and the plants grow. Calcium and magneisum levels will drop but chloride and sulfide levels will only drop slightly. This change in chemistry will drop PH and GH. You can counteract this by putting a natural decorative sea shell in the tank. Sea shells are mostly calcium carbonate. They will react with the excess chloride and sulfate and push the PH up to very close to a ph of about 7 and help stabilize GH.

Thank you and yes, only living plant is the Java Moss which I took from my Fire Belly frog tank. I did the tank using fake plants for now because I have the mystery snail which in a small previous tank ate my living plants. I do prefer all live, but was hard to keep anything with the snail so in this small 10 gallon, just wanted some cover. I’ll review all of the above and see what I can do. Thank everyone again!