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As you can see my little planted tank looks OK. However the pH is 8.1 during the day! and 7.6 during the night.

I recently added a bag of "Eco Complete Planted Aquarium Substrate" to the present substrate, which was "Flourite" and sand.

I doubt this has caused the rise (the pH used to be 7.2). I think the plants are enjoying their new substate, and are removing all the CO2 from the water with their growth?

I've added a cheap CO2 system - the "TetraPlant CO2-Optimat"



This seems to have done nothing to reduce the pH.

TDS is 160ppm. can i get away with reducing this further? i'm a bit hesitant, as i don't want huge day/night pH swings.

I don't really want to resort to applying acids, as the tank is only 15g, and again i fear for big pH swings during water changes etc.

i don't want to use peat as i think the tannins will attenuate the lighting (compromising the plants), and i'm not adding carbon to remove the tannins, as i think this is complicating the situation too much!


Are my deductions correct, and what can i do?


Thanks.

How long has the aquarium been set up? It normally takes about 90 days for a new tank to stabilize (with or without fish) and find it's equalibrium. You've such a small volume of water, it will experience wider swings than say, a 55 gallon or larger tank.

Every planted tank has different pH between day and night, especially if Co2 is used at night, which it shouldn't be. My Co2 systems are on timers, and shut off at lights out. I aereate most of those tanks at night to help keep the 02 level higher and the ph more stable.

If you don't want to use peat then carbon route, you can purchase one of those ion exhange water softning pillows in a canister filter. They take time to work, but they do work, without staining the water. Problem with those, however, you have to keep a close eye on your pH while using it so it doesn't drop too far too fast in your small tank.

The substrate you put in is the same I use in some tanks. It is simpley a chelated iron containing clay, and will have no bearing on your pH.

I like your design; very jungle-like. What fish do you or are going to keep in it?

Good luck,
Dave

I'm glad you like it, the "jungle" look is what i'm after.

It's been set up for about 4 months.

softening water is no problem, i have an RO, but i don't know how soft i can go before problems start.

The CO2 system is really simple, you fill the in-tank dispenser from the bottle each morning, and the CO2 diffuses out of the permeable membrane. it empties by the time the lights go off so it doesn't release at night.

fish are:

6 Nannostomus "coral II"
5 Microctenopoma ansorgii (very small)
6 Corydorus pygmeus
4 Corydorus hastatus
4 Ottocinclus sp
1 Farlowella vittata
1 Ancistrus sp. 3
1 Macrognathus circumcintus
1 Common Plec!!!!!! he came "free" in a bag of plants i bought! (he'll be moved soon, along with the ancistrus and possibly the Farlowella)

Softening the water removes the buffering capacity of your water that is keeping your pH higher than normal, thus dropping the pH. By the way, have you tested the water that come out of your tap lately? The water company may have changed its parameters.

You should aim for neutral to slighly acid pH with the fish/plants you have (I especially like the Hydrocotyle trailing about) . About 6.8, gh about 6 and 77 degrees would suit them quite well.

Plants should stablize a tank, epecially in the profusion in which you have them. They will stablize in time with the new nutrients for their roots, and they could adjust your pH to more stable levels automatically. Try taking readings day and evening for a couple weeks to see if the roller coaster starts to subside. You could also try suspending the Co2 for a week or so, as that is a recent addition, is it not?

Have you cross-checked your ph reading with another brand kit and/or electronic monitor? Eco-complete and Co2 are not your culprits. Something is hardening the water, buffering it up to a higher pH, and I seriously doubt its the plants.

I know its tough to be so careful with 15 gallons of water; its small tanks and their varieables that magnify so strongly that turn so many newbies off the hobby.

Dave

Yes the Hydrocotyle does look nice, it's only been in a few days though. I don't think it'll last long though, the otos seem to prefer eating it to anything i give them

So what value can i take the KH down to before the pH swings become too great?

Tap water isn't an issue, as i use RO. I add Kent "RO Right" (GH) and "pH Stable" (KH) to get about 130ppm TDS. The proportions are about 60ppm of each. The remaining 10ppm is the value of the RO water, which i gather is the sodium chloride that's small enough to get through the membrane.

How shall i mix up the water to get the right pH value?

My initial post said that the TDS was 160ppm, but that was from memory, and i've checked my records and it's 130ppm (8dH) Unfortunately my TDS meter went haywire and is now broken. my liquid test reads 60mg/l CaCO3 (3.36dH), so i don't think there is anything else buffering the water.

My pH is tested with a digital meter that i calibrated the other day.

The CO2 has been running for a week. I got it to try and reduce the pH! and help the plants.

I'll gradually reduce the KH, keep testing and see what happens.

I started with 2 strands of Hydrocotyle sp. I have to cut it back a lot because it grows across the top of the tank. I have it in 4 tanks now. It seems the more you cut it, the more it grows. Otos make holes in the leaves of the Hydrocotyle every now and then. The leaves are rather thin. I also use it as a floating plant in 10 gallon tanks.

Barbie made a suggestion to me about the RO water and it's worked well. I add a little tap water back into the RO water until the TDS is where I want it. It doesn't take much for me because my water is very hard. My pH is still around 8.0, so I add a small amount of the Seachem Acid Buffer. This has no phosphates, etc. This is how I reconstitute my RO water. The pH remains constant at 6.8 for around 7-8 days now using this method. Prior to that, it was all over the place: from 6.2 to 8.3. I keep my TDS a little higher, around 200. Water out of the tap can go as high as 850-900. We humans don't drink it, either.
Amanda

it's really odd. i use the same water for my big tank, and like yours the pH is about 6.8.

I've got some kent "pH Down", but i'm a bit wary to add this to the water in such a small tank, but i think i'll have too.

I just read this...

In a heavily planted aquarium, alkalinity may be depleted by plants in need of a carbon source. In such cases the plants will chemically break carbonate and bicarbonate ions down to utilize the resultant CO2 for incorporation into cell mass (biogenic decalcification), and as a result pH may actually increase; the process reverses itself at night when plants are producing CO2, eventually causing pH to drop.

I think this may well be what's happening in my tank.

more CO2?

Racoll,

Go to http://azgardens.com/newCO22.php and scroll down to Co2 equilibrium. They explain your problem far better than I can, and how to solve it.

Good luck,
Dave

I never saw your posted KH values. If you are using ro water there might not be enough carbonate harness to carry co2 in the water. Maybe you need to buffer your water to a higher kh so it can carry more co2. That may help stabize your water. You might want to check out this link for kh/co2/ph relationship chart.


Cheers, Whitepine

IMO the very first thing you need to do before starting to mess with your tank chemistry, is verify that your pH test is anywhere near accurate.
pH tests have got limited shelf life, and especially pH sticks/paper is notoriously inaccurate even when fresh.

Mike_Noren, I have tested with a brand new hanna digital pH meter, which i calibrated the other day.

Whitepine and djw66, Thanks a lot for the info.

Just to clarify, my TDS is 130ppm and half of that is KH, so my KH is 3.36dH.

So what i've gathered from all that info is i need to INCREASE my KH, and INCREASE my CO2 to get the pH down, and optimise plant growth.

So at the moment i have a pathetic CO2 concentration of 1.0 mg/l. So i will have to raise that to about 10 mg/l.

It seems counter-intuitive to the general doctrine that your pH goes down when KH goes down.

I'll give it a go.