pH never above 6 - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 7 Old 11-10-2012, 07:19 PM Thread Starter
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pH never above 6

I have a 40 gallone freshwater tank. It has been running for many years without problems. I have 4 clown loaches, 5 red eye tetras, 6 cardinal tetras, 3 pristella tetras and 3 glow lite tetras. The tank is planted and I have a couple of moss balls. The plants do well and I prune when pruning is needed. I just added a floating water sprite. I add in Fluorish supplement every 3 days. I do a gentle gavel surface vacuum every couple of months when there is debris floating on the surface but I do not do any deep vacuuming. I have foam blocks, NitraZorb and PhosZorb, and Aquaclear Biomax in my Fluval canister filter system. No carbon. I do a 50% water change weekly with R/O water that I prep. The R/O water has a pH of 6.4, GH of 5-6 and a KH of 1. The tank water consistently runs pH less than or up to 6 (the test kit only goes as low as 6), GH 5-6, KH 1, Phos 0, Ammonia 0, Nitrite 0, and Nitrate 20. I don't measure O2 or CO2 but I look at a chart I have that estimates the CO2 based upon pH and KH parameters.

My questions are:
1.) do I need to worry about the pH being low and the KH being low?
2.) Does my adding in the Fluorish every 3 days cause the pH to run low? I don't have any plant tabs I put in the tank.

I have not worried much about the parameters since they have been running stable for a long time, the fish do well (one clown loach I have had for 7 years and it is still going strong) and the plants seem to grow well (although I do not have any luck with bamboo in the tank).
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post #2 of 7 Old 11-11-2012, 07:55 AM
It would 'seem' that your tank water is very acidic, but if the plants and fish are doing so well, why worry? Don't fix what isn't broken. If you were to have issues of erratic behavior signaling stress and/or fish loss, then I might suggest adjusting the treatments you're using to increase the pH in your RO water.
Btw, just curious, why are you using RO water which is often used for SW mixes, but rarely in FW?

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post #3 of 7 Old 11-11-2012, 08:27 AM Thread Starter
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Thanks for the help.

Some time ago, I experimented with seeing what mix of tap H2O and R/O I could use to keep the tank's parameters stable. I have well water. The pH is ~7.7, GH ~7 and KH ~1. Some times I noted the nitrate up to 5 in the tap water. I seemed to find that if I mixed 1part tap water with 9 parts R/O water, that the pH ranged from 6.4 - 6.8. I found using R/O water with Replenish gave consistent results with a pH of 6.4; the GH would be 4-5 and the KH would be 1. I juts stuck with the R/O water ever since since I didn't want to create too much shifting of the pH in the tank. Someone told me to run the tank's pH at 7.0 but if the pH of my tank is no higher than 6 and the fish/plants are doing well, I didn't want to make big tank changes.
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post #4 of 7 Old 11-11-2012, 08:28 AM
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That's some .... odd R/O water, as it should be neutral (pH 7, 0 GH and 0 KH). Are you adding anything? EDIT: You replied at the same time and answered this.

Flourish will not change your pH. It is dropping so low because your KH is so low, and the natural processes of the tank (bacteria breaking down wastes, etc). If you used pure tap water, it would also drop from the initial 7.7 to something less. My own tap water is 7.4 with a KH between 1 and 2 degrees, my tanks all sit at a pH of 6.4 now that they have settled.

All the fish you list are soft, acidic water fish, so as long as the pH isn't too far under 6 I don't see a problem. You would have to find a different pH test to know for sure.

If it becomes a problem, you can put a very small amount of a calcareous substrate into your filter (and by small, I mean real small). It will dissolve and will raise everything (pH, GH, and KH). You need to use a small amount because otherwise it will swing it up above 7 and make your water hard, which none of your fish will appreciate.

Last edited by Geomancer; 11-11-2012 at 08:31 AM.
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post #5 of 7 Old 11-11-2012, 09:36 AM Thread Starter
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I replaced my R/O unit a couple of months ago because the old one broke after having a number of replacement parts fixed over time. With a batch of today's R/O water, the Ph is 6.6, GH 0 and KH 0. Before the old unit broke, I would add in Replenish to get a pH of 6.4, GH 5-6 and KH 1. I used to use Seachem Equlibrium, acid buffer and alkaline buffer. I witched to Replenish on the advice of a friend who uses it in his tank with success.

Any way, I could try mixing tap water with R/O water again to get the right ratio/mix. Is it easier or better to use the R/O water and add in the chemicals to adjust it, as I have been doing? Is a KH of 1 a problem?
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post #6 of 7 Old 11-11-2012, 11:50 AM
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Perhaps I can add a bit of explanation to what has already been mentioned. And offer a suggestion or two at the end.

The water in any aquarium will naturally become more acidic due to normal and continuous biological processes [bacteria breaking down waste, etc]. Carbonate hardness (the KH or Alkalinity) impacts this, so the higher the KH the less acidic. Adding calcareous substances (sand, gravel, rock composed of calcium and magnesium) will raise the GH and pH. Adding wood, peat, leaves that release tannins will tend to lower the GH and cause acidity, thus lowering the pH. All of these processes are inter-related. For further reading:

I have near-zero GH and KH in my tap water, and the tanks used to run at 5 or below, unless I specifically targeted the tank by adding some calcareous gravel in the filter. This depends upon the fish. Those in my pH 5 tanks are wild caught fish like cardinals, pencils, etc, and this is where they belong. For some reason, all my tanks are now running in the 6's, and I suspect this is due to something being added by the water folks to raise the pH. Won't get into that.

To the additives. The best way to maintain stability is with regular water changes. In your situation, I might consider just using the source water, as the GH at 7 and KH at 1 is perfect for soft water fish and live plants [the latter need some GH for the "hard" minerals which are too minimal in commercial fertilizers like Flourish]. This would avoid the need for Replenish, which by the way is not the best product for the purpose. Equilibrium would be better, if you continue using RO with an additive.

There is no problem with the current numbers. The pH is obviously stable. The fish are right at home in this water.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #7 of 7 Old 11-11-2012, 06:48 PM Thread Starter
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I guess I won't fix what is not broken if the fish and the plants are OK.

From today:

R/O water without Replenish added to it: pH 6.5, nitrate 2.5, phos 0, GH 0 and KH 0.
Tap water: pH 7.4, nitrate 30, phos 0, GH 8 and KH 4.

Usually when I add Replenish to the R/O water, the pH is 6.4, GH 5-6 and KH 1.

I don't use tap water due to fluctuations in the nitrates, perhaps due to the farms I live next to.

It seems the Replenish adds in GH and not much KH.

Thanks for everyone's help.
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