KH dropping over time

[stevie D]

The kh out of my tap is around 3 degrees. The ph is greater than 9 out of the tap. Over a few days, the ph drops to about 7.1 when in a tank. I have 2 ph meters that i have check all my ph measurements on. My GH is about 6 degrees. This tank is a 26 gallon bowfront.

I've noticed that my KH drops to sometimes below 1 degree over a week or 2. I do regular 50% water changes once a week and KH still never get over about 1.5 degrees (i am using a calibrated test kit and use double the amout of water to test to improve accuracy). I add bicarb sometimes to bring the kh to right around 2-2.5 degrees when i see it fall below 1. I also also add 5ml of mixed P/K and 5 ml of CSM+B as per ei dosing for a 26 gallon tank. I do not add any N because there is between 15-25ppm during the week due to fishload. I have ecco complete red as my substrate. I run pressurized co2 with a controller to acheive around 30ppm of co2 using the cal aqua double drop checker. The ph of the tank after co2 injection is right around 6.

I don't add anything else, there are no rocks or anything else that could effect ph/kh that i know of in the tank. I used to add PH down to get the tap water down some before putting in the tank, but that was well over 2.5 months ago, and i figured with all the water changes this would be gone from the water, but i'm not sure. Any reason for my KH to continually drop the way it does? Is this at all normal?? The only reason i add bicarb is because over time i'd have to lower my ph to around 5.6-5.7 when it drops to keep 30ppm of co2 in the tank. While i know this probably isn't bad for the fish as it's a discus/south american setup right now, it still seem kinda low when the ph gets to the mid 5's.

I do have good circulation in the tank (Eheim 2115 and a penguin 550 powerhead) and i inject co2 into the outtake of the Eheim's spraybar using an aquamedic reducing t which has been working well.

I do not mind having to add the bicard to keep the ph/kh up, just want to find out why it is dropping as i haven't heard this to usually be the case. Oh, at water change time the only thing i add is prime. I also about once a month use excel at a slightly higher dose everday for a week to controll algae, which there is very very little, and practically none after excel treatment. Lighting is not important in this case and i don't have any issues, but i run 2 24 watt t5's for 10 hours with a noon burst of 4 bulbs for 4 hours.

I would like to not have to alter the ph controller/or add bicarb to keep the co2 consistant, but i have no problems doing either in a controlled enviroment, and have never had a problem with pressurized co2.

Is this not even a problem? Should i just do water changes and let the kh adjust to what ever it will over time and just set the ph controller at a lower ph?

This is for anyone to answer that has any advice, and sorry for the post being soo long, i just wanted to be complete and list everything that is goin on in the tank. I am an engineer at heart so i really get into the testing side of the hobby to varify what i am observing, but do realize it's how the fish and plants are doing is the important thing. I also keep different species of snails in my aquariums and was wondering if a very low kh will ultimately have an effect on their shells or health.

Thanks!!

Stevie D

 

[stevie D]

SO this happened again. It has been about 9 days since my last water change held off intentionally and i noticed my drop checker starting to turn more blue than green. So i check my kh, and sure enough, it is about half a degree kh. I really don't know what could be causing this. I added bicarb right after last waterchange and raised the kh to 2.5. A week later it's less than one.

I'm wondering if this eco complete red that i got which is before they released the "red" version of their substrate is doing this.

Anyone have any ideas? It seems like i will have to adjust my ph controller every few days to keep consistant co2 in the tank.

Stevie D

 

[VaughnH]

You have found the Achilles Heel of pH controllers. They control CO2 without regard for what the KH is.

If you were not using the controller, but just maintaining the bubble rate that gives you the amount of CO2 you need in the water, this would not be a problem. The drop in pH from adding CO2 is not a problem for the fish or anything else in the tank. Long before the CO2 could lower the pH so much as to be a problem, if it is even possible for it to do so, the CO2 itself would kill the fish.

 

[Tom Barr]

The KH and the pH work well if that is all there is to the issue for CO2, however, that's not the case.

Another Achillies Heel.
I've found pH pretty poor for a reference for CO2 inside a planted tank.

I've used dissolved CO2 meters to measure the differences and they are quite large within a large well circulated aquarium with plants.

pH is typically FAIRLY MUCH THE SAME THROUGHOUT HOWEVER.
So......in theory it should not be, but that's theory vs real field test.
I've long suggested and said this is true, but with the pH valves, I had no data for support, with the CO2 meter, I certainly do and it's no surprise to other researchers either.

You need the right tool that addresses the issues within the system to show the correct measurement you see. CO2 in this case, not pH.

I'd say if the KH is falling this fast, your plants are going after the bicarb/KH, meaning that the CO2 gas addition is not as high as it should be.

You need more CO2/less light or some combo thereof.

Regards,
Tom barr
.

 

[stevie D]

Well beside the kh dropping, the tank is very stable. It seems if i keep the kh low the tank ph will have to be around 5.5 or even lower to acheive about 30ppm. Any reason this would be harmful to fish snails or shrimp over time?

Should i even bother adding bicarb at water changes? I have a 55 gallon that is cyclying with black eco complete that will essentially be the same setup. I'll have to see if it's something in the 26 gallon that is making the kh drop.

So I assume it's not the norm for the kh to change so fast is it?

Stevie D

 

[VaughnH]

I almost never check my KH, so I don't know how constant it stays. I used to add baking soda once a week, with water changes, to try to keep the KH above about 4 dKH, but I became convinced I wasn't gaining anything by doing so and quit. I'm not sure my KH kit even still works.

 

[Tom Barr]

The KH drop is an issue if you use a pH controller to add CO23, if not, then the KH can move around without affecting CO2.

If you do good sized water changes regularly, the Kh should be pretty close to the tap's.

Regards,
Tom Barr