pH 5.5, kH 1 ??!!

[hongrui]

i just obtained a new sera pH test kit today and measured my tank's (1) pH to be at 5.5.
i then took a pH reading of another of my tank (2) which was found to be 7.
next i took the pH reading of my tap water which was roughly 7.5

finally i tested my tank's (1) pH again which again was found to be 5.5.

kH readings for tank (1) = 1, tank (2) = 4 and tap water = 1

my question is what could have happened such to lower my tank's (1) by such a great amount. especially with no CO2 addition. i am planning to inject CO2 into both the tanks, but i'm worried that the injection would lower the pH to dangerous levels for tank (1). The CO2 level from the pH/kH for tank (1) is already at 90ppm+! which i think is impossible as the fishes show no sign of stress.

should i add in some coral chips to increase the kH but that would invalidate the pH/kH - CO2 chart right?

so what might have caused the low pH? and what should i do if i still want to inject CO2 into the tank? thanks!

Tank (1) Dimensions: 2' x1' x1'
Lighting 26w PL x 10 hrs
No CO2 injected
Fertiliser: Seachem Flourish x 5 ml per week
Additive: Seachem Prime
Water change frequency : 50% / 2 weeks, last WC on 10/7
Tank Temperature : 27C
no drift wood, 3" of river sand as substrate

Java Ferns tied to inert rocks, Ceratopteris thalictroides
30 x Boraras maculatus

[PeterGwee]

Do you use peat in the filter?

Regards
Peter Gwee

[hongrui]

no peter, no peat in the filter. it's a cannister btw. just sponge and biohome.
the tank has been up and running for 3 mths.

previously i was using one of the 'dip-stick' pH testkit and the lowest value measurable was 6.4. my previous measurements with the old test kit has always been about 6.6. last check was maybe 2 weeks ago.

not till today have i realised that my actual pH is so much lower.

[PeterGwee]

Something funny there if there is no peat. I suspect the pH test kit then. If you have the dough, get a pH test pen and calibrate it before using should tell things much better.

Regards
Peter Gwee

[hongrui]

A pH test pen would be out of budget. think i'll try and lend one or 2 more pH test kits and see what kind of measurements i get.

i'll update after i get my hands on a couple of test kits and getting the measurements.

thanks peter

[bclee]

It is entirely possible for pH to be 5.5 when the KH is very low. I assume that you come to the conclusion the KH = 1 when the first drop of the test kit already showed you the changed colour. This may mean that KH =< 1. Just raise the KH up to about 3 with baking soda (not baking powder) aka sodium bicarbonate, proceed with CO2 injection. You can add coral chips too, it will not affect the reading from the KH/pH/CO2 chart, because coral chips are mainly carbonates. (The reading will be off only when you add non-carbonate buffers.)

BC

[taz_boy]

i agree with bclee,
there maybe some problem in ur tank(1), the best is to up ur KH level and test ur PH level subsequently, that would be good.

[hongrui]

thanks bclee and taz_boy.

then i'll probably dump some coral chips into the filter when i get home tonight and maybe add some baking soda over the weekend if the kH hasn't increase by then.

[taz_boy]

thanks bclee and taz_boy.

then i'll probably dump some coral chips into the filter when i get home tonight and maybe add some baking soda over the weekend if the kH hasn't increase by then.

no problem,
a good KH value would be b/w 3-5.
and do take note the proper way to add baking soad into the tank, not just dump the powder into the water........

[juggler]

hongrui:

For tank (1), maybe there are decaying plant matter too that's bringing down the pH? You don't have any soil/base fert under the 3" of river sand? How long has this tank been since setup?

For tank (2), the 7 pH and 4 dkH may indicate there's some carbonates in the water. Do you have coral chips in there or add baking soda to this tank?

[hongrui]

hi juggler,

for tank (1), there's no visible decaying matter, no base fert also. Been relying on column fertilisation. It's been set up for 3 months plus.

for tank (2), yes, there's coral chips in the tank.

[juggler]

It is entirely possible for pH to be 5.5 when the KH is very low. I assume that you come to the conclusion the KH = 1 when the first drop of the test kit already showed you the changed colour. This may mean that KH =< 1. Just raise the KH up to about 3 with baking soda (not baking powder) aka sodium bicarbonate, proceed with CO2 injection. You can add coral chips too, it will not affect the reading from the KH/pH/CO2 chart, because coral chips are mainly carbonates. (The reading will be off only when you add non-carbonate buffers.)

BC

Baking soda by itself is alkaline. So it will not only raise the kH but the pH as well. So neutralising the acidity at the same time?

hongrui: There's another good article to read
Chuck's article: Measuring CO2 levels in a Planted Tank.

[bclee]

Baking soda by itself is alkaline. So it will not only raise the kH but the pH as well. So neutralising the acidity at the same time?

hongrui: There's another good article to read
Chuck's article: Measuring CO2 levels in a Planted Tank.

Strictly speaking... what we are measuring as KH is actually alkalinity. Raising KH will always raise pH. The relations between KH (CO3--/HCO3-) and pH (H+) and CO2 is as follow

2H+ + CO3-- <--> H+ + HCO3- <--> H2CO3
CO2(aq) + H2O <---> H2CO3

BC

[hongrui]

thanks for the link, juggler.

adding baking soda would increase the pH and kH in my tank, so what kind of increase should i target over the next few days so as not to stress out the critters?

i've read from one of the stickies here not to increase kH by more than 2 units in 24 hours. what about pH? what kind of increasement would be safe? 0.5 units per day?

just wanna be careful of my dosing of baking soda. i don't want a pH swing in the tank.

[taz_boy]

thanks for the link, juggler.

adding baking soda would increase the pH and kH in my tank, so what kind of increase should i target over the next few days so as not to stress out the critters?

i've read from one of the stickies here not to increase kH by more than 2 units in 24 hours. what about pH? what kind of increasement would be safe? 0.5 units per day?

just wanna be careful of my dosing of baking soda. i don't want a pH swing in the tank.

dun really need to worry much abt ph swing la.......mine always swing between 6.4 to 7.0, cos i using my DIY.
true enough, maybe monitor ur KH level a bit, dun 1 time wack from kh 1 to kh 4, may have some effect