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Another Low PH Question

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Offline Andy The Minion

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Another low pH question
« on: February 04, 2018, 02:47:18 PM »
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I have just checked my large tanks pH having done a routine weekly 40% water change yesterday. Today I was working my way round checking the other tanks and found this tank is at 4.3 pH (I checked the cal on the probe) A drop test also showed low, somewhere less than the 6pH minimum but the colour wasn't massively different to the 6.0 colour
The water is very soft and has been running very stabily at 6pH 0.5kH in the past so I had stopped checking pH on a weekly basis. I also checked the kH and it has also dropped to below 0.3 so I can understand why pH might drop.
The strange thing is everybody is looking happily, colourful and lively with one pair starting to spawn and another guarding eggs so it doesn't appear to be bothering the fish.
I was wondering if pH probes can be thrown off by other factors in the water (the probe is temperature compensated and not more than 3C higher than the calibrated temperature)

The only other thing I did yesterday was to removed 8 fish (about 60-70cm of bio load leaving 100cm in a 500litre tank with a sump) If anything I would expect a higher pH because the respiration levels have reduced.

So given that this is a South American Cichlid tank and the water is intended to be soft and acidic I will monitor the water and fish with some Sodium bicarbonate on hand if anything changes but from the lack of reaction of the fish would you think is this a problem or an instrument/measurement failure?

Offline Sue

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Re: Another low pH question
« Reply #1 on: February 04, 2018, 02:58:08 PM »
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To be honest, I've never had to deal with very soft water and low pH. If the fish seem OK, I wouldn't worry too much. A pH that low won't harm south American fish though a pH change that happens quickly might.

And I would not use bicarb in a tank that has fish. It adds a lot of sodium to the tank and soft water fish are not 'designed' to cope with this. The best way to increase KH is by using dolomite which contains both calcium and magnesium, unlike limestone which contains just calcium. It is CaMg(CO3)2

Offline Andy The Minion

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Re: Another low pH question
« Reply #2 on: February 04, 2018, 03:44:06 PM »
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Thanks @Sue and thanks for the Dolomite tip, it's the first time I have seen that suggestion. Meanwhile back at the bleeding ranch the plot thickens, I just calculated the CO2, using the same pH probe in my planted tank and if the pH reading were true then the CO2 would be 120ppm which is lethal, and again the fish are fine. This is the third pH probe I have had, I sent the one back because it would drift 0.5pH in 30 seconds in 7.0 buffer solution. I will give this one another chance and actually recal it rather than just take a reading in the buffers, if it still mucks me about then its also going to go back :(

Offline Andy The Minion

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Re: Another low pH question
« Reply #3 on: April 29, 2018, 06:43:41 PM »
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@Sue I have finally got on top of my low pH :)
Initially I put the suggested dolomite in the water conditioning wheelie bin, it arrived as a crushed coarse grit/powder sold for soil conditioning. The immediate result was very cloudy water which initially concerned me, but after a few days it had settled but still coated all the surfaces with a whiteish layer with the bigger solids on the bottom. The water was however clear enough to be used. The kH had increased a bit but it was still well below 1dKh, probably because the tap water is only just acidic.
I had originally planned on putting a bag in the sump with the thought that as the tank water became acidic the dolomite dissolution rate would increase and balance out the KH / pH. The cloudyness put a stop to that plan and a retest of the tank water at the end of the week showed the pH was still falling (4.6 if I believe the pH probe)
I left things like this for about 6 weeks to see if there would be gradual improvement - I don't think I was being cruel because they are South American Ciclids, in good health and have being growing rapidly and successfully breeding in these conditions.
However, this still seemed too risky to continue and I had a fairly major plan b which has I think solved the issue. [Yes everybody, I know I could constantly use a commercial buffer but that would be cheating :)]
I had originally put a hidden drain pipe up through the floor when I installed the tank to make water changes easier, so I have converted the tank to a trickle system. I have a bank of three 12" water filters and fitted carbon blocks in all of them to remove chlorine (lot of carbon, tiny flow, no Chloramines) The water feed enters the tank at about two drips per second and at this rate does a 100% water change over the week. The pH is now stable at 6.0 plus as a side benefit the Nitrates levels are flat and very low so I'm sure the fish will appreciate it.
One thing I immediately noticed, a 100% change by drip is not the same a weekly partial change. It is just a constant very slow dilution so you don't get anything like as efficient Nitrate removal as a big change - otherwise my NO3 levels would be falling (a 40% weekly change would normally keep this tanks NO3 levels flat) Using this this logic I would assume 'everything else' that a weekly change does for water quality is also less effective and I think I will continue with smaller bi-weekly changes with the dolomite flavoured water.

Offline Helen

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Re: Another low pH question
« Reply #4 on: April 29, 2018, 08:43:58 PM »
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In researching my Seneye I read that electronic pH probes can be unreliable in soft water. I'm not too clear on the technical details but I think it is something to do with the chemicals that cause hardness are needed for the acidic components to behave (electrically) in the way that the probe understands. Does that make any sense?

Apparently with really soft water test strips are the most reliable method of testing pH - providing you have a good enough quality test strip.

Offline fcmf

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Re: Another low pH question
« Reply #5 on: April 29, 2018, 10:08:04 PM »
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This is all very interesting, AtM - thanks for that.

Apparently with really soft water test strips are the most reliable method of testing pH - providing you have a good enough quality test strip.
I use JBL or Tetra test strips as I find them very good for nitrite and nitrate, struggling to decipher the liquid-based equivalents - also handy that they have a chlorine test on them. Interestingly though, I find they give a much higher KH and GH reading but a much lower PH reading than the water company and liquid-based kit results (each of which are similar to one another).

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