pool filter sand vs. play sand

[dw1305]

H all,

As a scientist I care about accurate absolute measurements. As an aquarist some reasonably proxy that tells me if my tank is stable or drifting is good enough, at least for now.

That is really why I like the <"Duckweed Index">, it is a proxy that every-one can use, in nearly every tank.

I think, in an ideal world, every-one would want to know the exact parameters of your tank. The real problem for me is that people under-estimate the difficulties of getting meaningful measurements (nitrate (NO3-) values would be a prime example) for their tank, and then make management decisions based upon the test results.

When I started looking at this, I thought I would be able to make recommendations for kits etc to use, but the only meter, or test kit, that you can dip in, and get reliable results over a whole range of water parameters, was a conductivity meter.

I knew that biotic indices and bioassay organisms were widely used in water quality testing, and are robust techniques with a sound scientific back-ground. So the question was if you can't use tests, can you use an adapted biotic index? and I think the answer is you can.

It is possible to quantify water chemistry with the appropriate analytical kit. You've used <"anion-exchange column chromatography"> and there are other options like GC-MS, HPLC, ICP, AAS, ion selective electrodes etc., but the problem is that they are out of reach of 99.9% of aquarists, and it still doesn't address the measurement of dissolved gases issue.

I was struggling more with pH. In my very soft water the pH pens tend to take a long time to achieve a stable readout and if you move it pH changes again.

Yeah we've discussed soft / low-conductivity pH on this forum many times too - it's a hot topic with blackwater fish keepers! Darrel will tell you pH is irrelevant in very low-conductivity pH, since a tiny shift in the relative mix of ions can cause an apparent big shift in pH, without much biological significance. I'm not quite ready to call pH "irrelevant" (too many decades trying to understand and measure it) but he's sure got me leaning in that direction ... at this point I might tell you it's "not very important" in ultra-soft water. I like color dye pH tests, since they're cheap and dont rely on electric conductivity. Please do let us know how you like that low-range pH paper. Years ago I had a low-range liquid test (red-to-yellow; dont recall which dye) for that crucial 4.0 to 6.0 range that blackwater keepers cherish, below the bromothymol blue test range. Haven't seen those kits in many years for aquarium use, but i assume the dye still exists for other applications.

I'm interested in the result of this as well. The low range pH indicator was probably based on methyl red.
If the papers prove inaccurate there are options for pH in low conductivity water, ISFET pH meters are better, and you can raise the conductivity of the water with a neutral salt (NaCl is the normal option).

It has to be analytical grade NaCl, you can't use "table salt" because of the magnesium carbonate (MgCO3) added as a desiccant.

Regarding relevance of pH in soft water I first of all don't think pH swings as much as people say it might...... But a more relevant point may simply be that these fish are evolved to live in soft acidic waters. If pH fluctuations are part of life then life will have been adapted to them.

You definitely get <"large diurnal pH swings"> in vegetated water, even when the water is carbonate buffered, the more buffering the low the amplitude of the swing around pH8. These pH changes largely result from the changing CO2 (as H2CO3) : O2 ratio during photosynthesis. For fish from soft vegetated water, pH change is an every day experience . "Blackwater", with a lot of tannins and humic compounds, is buffered against pH rise, partially because it doesn't tend to have many plants growing in it.

At pH 5 you need 100 times more acid or base to change pH by 0.1 unit so that helps to stabilize it. Tannins and whatever was used to push the pH down will act as buffer as long as they are weak acids, e.g. not HCl etc. So part of the reason that very low kH water, with little carbonate buffering, is not a problem is that pH may really not change as much as we are made to believe........

It is back to pH as a ratio and a log10 value, we know we are dealing with very small amounts of pH donors and acceptors because we have water with very low electrical conductivity. As you say as you move away from pH7 (in either direction) pH becomes more stable (because pH is a log10 scale).

Maybe I need to put it in a filter so water get drawn through it. Or I need to find a peat that works and doesn't cost a fortune.

If you use peat you need sphagnum peat from an <"ombrotrophic mire">.

@regani (who is a chemist) uses hydrochloric (HCl) and citric acid (C6H8O7) to lower pH. Have a look at his posts in <"peat granules to lower pH...">.

cheers Darrel

 

[gerald]

My hardness and alkalinity out of the tap (Raleigh NC system, drawn from Neuse River) are both around 25-40 mg/L (1.5 - 2 degrees GH and KH), and pH is 7.6 to 8.0 (they add NaOH to reduce pipe corrosion). In tanks with a moderate fish load and more-or-less inert sand, the pH can drop to 4.0 or a little lower over several months, presumably due to acids from bacterial metabolism. Tanks with just a pair of very small fish (Apisto, Elassoma, Betta, Badis, etc) never got quite that low. (I used to have an ISFET pH meter; the probe wore out and I haven't replaced it). I'm not currently keeping any species that need pH < 6.0, so now I just use a bromothymol blue test, and add small amounts of aragonite/crushed coral in the filter after the initial buffering gets used up; just enough to keep the indicator dye on the slightly greenish side of yellow.

 

[ButtNekkid]

1. "Blackwater", with a lot of tannins and humic compounds, is buffered against pH rise, partially because it doesn't tend to have many plants growing in it. 2. As you move away from pH7 (in either direction) pH becomes more stable (because pH is a log10 scale).l

Hi Darrel,

Would you like to elaborate on these two points? Especially the 1st one.

 

[gerald]

While we're waiting for Darrel's response, I'll take a shot at #1: Weak organic acids (tannic, humic, fulvic, etc) ARE chemical buffers, which can react with (neutralize) either bases or acids to a limited extent. The scarcity of submersed plants in most blackwater habitats means they're not pulling much CO2 out of solution. Emergent and floating plants get their CO2 from air much more efficiently than from water. #2 is above my pay grade, sorry.

 

[dw1305]

Hi all,

While we're waiting for Darrel's response, I'll take a shot at #1: Weak organic acids (tannic, humic, fulvic, etc) ARE chemical buffers, which can react with (neutralize) either bases or acids to a limited extent. The scarcity of submersed plants in most blackwater habitats means they're not pulling much CO2 out of solution. Emergent and floating plants get their CO2 from air much more efficiently than from water. #2 is above my pay grade, sorry.

Apologies I've been away for a couple of days.

1. Is the reason that Gerald suggests. You have a lot of proton donors (acids) from humic substances, but very few proton acceptors (bases). In most situations you would have at least some reserve of carbonate hardness (base) but in the central Amazon basin, you don't. There are some references at the end of <"Humic substances">. The article is worth a read as well.

2. Point two relates to the log10 nature of the pH scale. You really need @regani to check through through this, but I think this is correct (there is a more complete explanation at "Water ionization....".)

We regard pure H2O as an electrical insulator, but that isn't entirely true and it disassociates into hydronium (H3O+) and hydroxide (OH-) ions.

If we think of H3O+ as H2O and H+ (a proton), in pure H2O there are 10-7 H+ and 10-7 OH- ions. The pH value is the negative log of the hydrogen ion activity (in dilute solutions activity and concentration can be considered to be the same), when you add a base (a proton acceptor) the H+ ion concentration goes down, and the pH rises, so pH8 has 10^1 more OH- ions, and the activity of the H+ ions has declined by a power of 10 from -7 to -8.

At pH9 we have 10^-9 H+ ions and there are a hundred (10^2) times more OH- ions then there were at pH7.

When we add an acid (a proton donor) the pH falls, at pH6 (10^-6) we have 10 times more H+ than OH-, at pH5 a hundred (10^2) etc. By the time we get to pH4 we have 10^-4 H+ ions and a thousand (10^3) times more than we had at pH7.

When we measure pH it tells the ratio between H3O+ and OH- ions, but it doesn't tell us about amounts. We can get amounts, but we have to use acid base titration. If we have an acid solution, and we have to add a large volume of bases to raise the pH, the solution is "buffered" against pH change. You have to add a large amount of proton acceptors to accept the protons in the solution.

cheers Darrel

 

[dw1305]

Hi all,
This is a more straight forward <"self-ionization of water"> reference.

cheers Darrel

 

[gerald]

dw said: "When we measure pH it tells the ratio between H3O+ and OH- ions, but it doesn't tell us about amounts".

If we know the pH, don't we also know the actual amount of H3O+ and OH-, since their product is always 10^-14 ?
As I understand, it's all those other ions reacting with H+ and OH- that a pH measurement doesn't tell us, but conductivity does.
In water with very few other ions, a small addition of acid or base can cause a big pH change.

 

[dw1305]

Hi all,

......If we know the pH, don't we also know the actual amount of H3O+ and OH-, since their product is always 10^-14 ?.

Gerald you are right, you always have a total of 10^-14 OH- and H3O+ ions, otherwise pH wouldn't work as a scale.

I know that we've been through the <"same thing before: Apistogramma Forums - TDS vs.....">, and you have corrected it before, so apologies for that.

As I understand, it's all those other ions reacting with H+ and OH- that a pH measurement doesn't tell us,.

Yes, that is what I meant, but I failed to write ~ "other ions". If you use the proton donor/acceptor acid definition (<"Bronsted Lowry acids">) you can work out if a salt is an acid or a base. It is more difficult with organic compounds, so I just google them.

This shows why NH3 is a base.

... but conductivity does.In water with very few other ions, a small addition of acid or base can cause a big pH change

Yes, that is right as well, the electrical conductivity of H2O is really small, so it is usually expressed as a resistance value for ultra-pure water. At 25oC you are talking about ~ 0.05 microS cm-1 for ultra-pure water and less than 10 microS for RO water. Any ions you add (including H+ ions) will raise the conductivity.

If you don't have any proton acceptors a small addition of proton donors will cause a major fall in pH.

A good example of this is the acidic reaction between CO2 and rain-water (H2O). Carbon dioxide is a soluble gas, but it only forms 0.04% (400ppm) of the atmosphere and only a very small proportion of the dissolved CO2 forms carbonic acid (H2CO3), but it is enough to reduce the pH from pH7 to ~pH5.5 (you can see the donated H+ ion on the left of the equation).

The only problem with using conductivity is it doesn't tell you which ions you have, and a neutral salt (from the reaction of strong acid and strong base) like NaCl will raise the conductivity, but not change the pH.

This is also discussed in the linked thread (from earlier) <"TDS vs hardness">

cheers Darrel

 

[ButtNekkid]

My mind implodes...

Darrel, your link to humic substances does not work.

 

[dw1305]

Hi all,

... Darrel, your link to humic substances does not work.

Let's have another go: <"Guest Blog Tannin Aquatics - Humic substances">.

cheers Darrel

 

[Bart Hazes]

Hi all,
Let's have another go: <"Guest Blog Tannin Aquatics - Humic substances">.

cheers Darrel

Interesting read. I have a jar of untreated peat sitting on my kitchen table to check colour and pH effects on my RO water. I've also experimented with tree bark. The one I had was cedar and it worked great (pH dropped to 4 or less and dark brown stain) but smelled like resin so I never dared to expose fish to it. A bit more reading indicated that there are deciduous trees that should be fish safe and drop pH but I haven't started hunting for them yet.

Regarding the author's description to keep a second duplicate tank to use for aging water prior to adding to the fish tank, I don't consider that necessary if you use pure RO water. If you do a 10% RO water change you at worst cause a temporary 10% decrease in concentration of compounds. A good downpour in the rain forest will likely do the same to the small creeks and puddles many of our apistos come from. In addition, I pre-soak oak leafs in my RO water tub so that when I need some extra leafs they are already water logged and no longer floating. It also means my RO replacement water has at least some tannins in it.

 

[dw1305]

Hi all,

A bit more reading indicated that there are deciduous trees that should be fish safe and drop pH but I haven't started hunting for them yet...........

Other than Oak (Quercus spp.), Alnus glutinosa is the <"traditional one used in Europe">.

I assume all Alders have similar characteristics, and I've added Alnus cordata and Alnus incana cones (which may be <"available to you?>") in the same way.

Magnolia grandiflora is another option, they sell the leaves for use in Dart Frog vivaria.

Have you seen <"All the leaves are brown">? It was written by Colin Dunlop a Scottish Betta breeder.

cheers Darrel

 

[aarhud]

I use oak leaves (white and red). I really wish I could find alder cones. I don't know if we have them in the Carolinas.

My parent's property has several large oaks. I went leaf collecting last week and almost "collected" a copperhead (Agkistrodon contortrix?) instead! I think fall is the best time to collect.

 

[gerald]

Tag alder (Alnus serrulata) is the common one throughout the Carolinas, mountains to coast. Look for it along edges of ponds, small streams, and wetlands.

 

[Bart Hazes]

I found alder in the river valley of Edmonton Canada. The most likely place to find it is along the banks of small side creeks where there is more sunlight and wetter soil. I can harvest alder cones in late Fall and early Spring when it is the dead dried cones. But stripping of bark will definitely not be allowed. Same with oak, harvest in Fall after trees have resorbed nutrients and the brown leaves have fallen off.
I just discovered that using a freshly fallen tree branch with partially dried out leafs attached in a tank is NOT a good idea, unless you want to grow infusoria. I did this in a new tank without fish and got a nice bacterial bloom followed by a rich brew of unicellular infusoria

I do not find that oak leafs do much in releasing tannins in my tanks. They are quite long-lived and degrade very slowly, much slower than catappa leafs, unless you have amano shrimp. These guys are 'leaf shredders" and just leave the midrib and largest veins.

 

[gerald]

Unlike western Canada, we have dozens of different oaks in the Carolinas. Some are thin and flexible and break down fairly quickly, like Northern Red Oak (Q. rubra) and some are stiffer, leathery and long lasting. My favorites for aquarium use are Post Oak (Q. stellata) and Southern Red (Q. falcata), both of which are long-lasting AND release good amounts of brown stuff. Sugar maple is good for growing infusoria, amphipods and shrimp, and I'm guessing it would probably make good blackworm or Dero food too.

 

[doinkmobb]

I've used pool filter sand in most of my tanks, it's clean, doesn't compact and just works. As an experiment, I have about 1/2-1" of play sand in my 33 gallon checkerboard cichlid tank. It took a lot of rinsing to get it reasonably clean and is easily stirred up. I definitely wouldn't add more than 1" and it wouldn't work in a tank with fish stirring up the bottom all the time (Geophagus). But for my application, it works.

In regards to pH and hardness and tannins...the only thing I worry about now is TDS. I throw in leaves (Magnolia grandiflora) and sticks until the water looks murky enough. I do a water change when the TDS goes over 50ppm. I'd have to guess that the pH is in the mid-high 5s. I was keeping a detailed log when I first set up my 75 blackwater, and I definitely saw a downward trend in pH as I lowered the TDS and increased tannins. Now that I know what works, I don't feel the need to get bogged down in the numbers.

From the article that dw1305 posted: "To provide an optimal simulation of these substances, it is of utmost importance to provide as varied a source of humic substances as possible, to include using multiple types of peat from different locations, various types of leaf material, different woods, etc... While any source of humic substance is better than no source, multiple sources are better than a single source."

That's an interesting idea. Maybe I'll see what I have local to me that I can add to my tank.