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Finally

Posted: 21 Oct 2020, 06:22
by Baardman
Finally got a RO filter going did my first changes did small 30% changes My L168 tank tds is down to 60ppm GH1 KH 1 but the ph is still stuck at 7.6 how long before i can expect it to stat dropping? Will the drop happen gradually? I do have lots of wood in the tank and also added some liquad tree leaves.

Re: Finally

Posted: 21 Oct 2020, 06:26
by bekateen
Congratulations on the RO unit. As for the pH drop, I'd wait 3-5 days at least, depending on how long your wood has been soaking and how quickly it's releasing tannins.

God luck, Eric

Re: Finally

Posted: 21 Oct 2020, 07:39
by Bas Pels
You did aerate the RO water?

Remember, it is 100 % free of gasses when it leaves the unit. Aerating will increase the level of oxygen, but also thelevel of carbondioxid, aka carbonacid, which will decrease the pH.

Normally one takes at least 12 hours for aerating, and in case of the nead to decrease the pH, you could add peat to the water to help this.

Still, in all tanks there are many, many parts on solids which are in equilibrium with the pH. And if the pH decreases, these will react, basically increasing the pH to very close to the original value. Therefore, pH changes take a lot of timu, even if the added water is more acid then you aim for.

Re: Finally

Posted: 21 Oct 2020, 08:19
by Baardman
Thanks ill wait +- 7 days and test again

Re: Finally

Posted: 21 Oct 2020, 13:50
by dw1305
Hi all,
Baardman wrote: 21 Oct 2020, 06:22Finally got a RO filter going did my first changes did small 30% changes My L168 tank tds is down to 60ppm GH1 KH 1 but the ph is still stuck at 7.6 how long before i can expect it to stat dropping? Will the drop happen gradually? I do have lots of wood in the tank and also added some liquad tree leaves.
It should be fine. I wouldn't worry too much about the pH.

When you have any carbonate buffering (dKH) the pH is a reflection of the CO2 ~ carbonate equilibrium, which is controlled by the level of atmospheric CO2 (currently 411 ppm and rising rapidly). At 400ppm CO2 the pH value is ~pH8.

Because you don't have many ions of any kind (ppm TDS is estimated from electrical conductivity, and 60ppm TDS is equivalent to about 100 microS.) when you start adding weak acids (proton (H+ ion) donors) those protons will be accepted by a base (a proton acceptor) and neutralised. The pH won't change until all those bases (the dKH) are neutralised.

Once you have enough humic acids and tannic compounds in the water pH will fall, and when you are around pH7 (equal numbers of proton donors and acceptors) that fall can be rapid. That is one of the issues with pH it is both a ratio and a log^10 scale, so pH6 is a ratio with one order of magnitude (10^1) more proton donors than acceptors, pH5 has two orders of magnitude (10^2) more etc.

pH doesn't tell us anything about amounts, just ratios, buffering (alkalinity as an estimate of dKH) tells us about amount of bases and we can only interpret pH if we have an estimate of dKH as well.

This also means you can't extrapolate from hard water (high dKH) to soft water (low dKH), and pH can never be stable in really soft water (unless you add phosphate buffers etc. which are totally pointless). This is the same in the aquarium and in nature, and if you have soft vegetated water you will get huge diurnal (diel) pH swings as the CO2 (acid):O2 (base) ratio changes during photosynthesis.

Because of this I use a slightly different approach, large changes in pH are only likely to be damaging to soft water fish if they are accompanied by large changes in water chemistry. Because of this I monitor conductivity, and I just keep that within a range of about 80 - 120 microS. I have a hard tap supply (~18 dGH/18 dKH) so I can add tap to my rain-water (analogous to RO in this instance) to bring the conductivity up and DI water to take it down.

cheers Darrel

Re: Finally

Posted: 21 Oct 2020, 14:53
by Baardman
So what your saying it will take time to neutralize, I will try to keep my tds count stable between 50 and 60 I really need it to go down to the low 5's. On the butterfly plecos the ph influences the incubation time of the eggs if its to high they hatch prematurely. Thanks for the massive reply slowly making sense

Re: Finally

Posted: 21 Oct 2020, 17:24
by dw1305
Hi all,
Baardman wrote: 21 Oct 2020, 14:53So what your saying it will take time to neutralize, I will try to keep my tds count stable between 50 and 60 I really need it to go down to the low 5's. On the butterfly plecos the ph influences the incubation time of the eggs if its to high they hatch prematurely. Thanks for the massive reply slowly making sense
Yes, if you get down to 50ppm TDS then the tannic and humic compounds from the Alder (Alnus spp.) "cones", Oak (Quercus spp.), Indian Almond (Terminalia catappa) etc. leaves will eventually depress the pH, they will also add antimicrobial substances that will reduce bacterial activity.

That is why I like conductivity as a measurement, it is a nice straight forward linear scale and when you get down to below 100 microS you know you don't have much carbonate buffering, because you don't have many ions of any description.

I think the practical application of buffering and pH are conceptually quite difficult, because they aren't straightforward subjects.

Have a look at "All the leaves are brown" written by Scots aquarist Colin Dunlop.

cheers Darrel

Re: Finally

Posted: 23 Oct 2020, 11:46
by Shane
Thanks for the link Darrel. Good article.
-Shane