Ph levels goes down often

[josephfu]

Hi,
Why would Ph go down slowly on a daily basis. For example after a 50% WC with Ro water and preis minerals its 6.8 but in 2 days the max, it goes down to 6.0

The tank size is 55gallon and have 6 adult discus in it. No co2 added, I just feed frozen BF 3x a day.
output from Ro filter is 0Gh and 0Kh

seems preis minerals do not have any kh buffer in it and so ph is not altered.

Previously I used to use jbl quadur but used to end up with a kh of 2 and ph 7.3
When I mixed both minerals (at a lower dose) to get to around 1kh, the downward shift of the ph is still there , although at a slower rate. in 3 days it went from 6.8 to 6.2

is this behaviour normal at 2Kh of buffering ? I would like to have a slightly acidic water but seems its quite difficult to get, although I use just RO water without tap mix.

do I have to keep doing water changes every 2 days to keep the ph in acceptable range 6.5>6.8 ,because this is what I am doing at the moment.

not sure if it is a good idea to does some sodium bicarbonate between water changes as I don't know the effect of accumulated sodium in the tank.
Or maybe what I can do is alternate the water changes? for example do one 40% with preis minerals and the next wc do a smaller wc 25% with aquadur? ( like that I will replish the kh mid week with the proper mineral mix)

or maybe a little crushed coral?

I don't wish to use my tap water due to high nitrates in it.

maybe someone can give me an 2nd opinion as I am still quite new to discus.

I can afford to do 3 40% water changes a week but ideally I don't do them just to fix the ph issue.
thanks

[Ryan925]

Curious why you are trying to keep the low ph? Maybe a 50/50 tap to ro mix would be better?

[josephfu]

Good question
Tap is 7.8ph and tds 900 nitrates >40ppm. I am trying everything to avoid tap. Apart from the RO system is a fast one so its easier to use and I don't need to age water and waste goes back to the roof tank. I used to keep a group of my discus at 7.3ph but was using aquadur. Someone advised me to use preis discus minerals but seems this has no kh buffer in it. This is when I started experiencing a faster fall in ph in between water changes.
I'm curious what other discus keepers do to keep a stable system with one or two water changes a week and a ph <7
still learning and trying to figure out how things are performed, but from what I can understand its difficult to have a good kh buffer like 3 or 4, with an acidic ph.
Maybe I should just keep it the simple way and stay at 7.3ph ranges.

probably I'm over complicating matters for nothing but I wanted to understand about certain things. I know chasing ph is a bad thing to do

[Ryan925]

Good question
Tap is 7.8ph and tds 900 nitrates >40ppm. I am trying everything to avoid tap. Apart from the RO system is a fast one so its easier to use and I don't need to age water and waste goes back to the roof tank. I used to keep a group of my discus at 7.3ph but was using aquadur. Someone advised me to use preis discus minerals but seems this has no kh buffer in it. This is when I started experiencing a faster fall in ph in between water changes.
I'm curious what other discus keepers do to keep a stable system with one or two water changes a week and a ph <7
still learning and trying to figure out how things are performed, but from what I can understand its difficult to have a good kh buffer like 3 or 4, with an acidic ph.
Maybe I should just keep it the simple way and stay at 7.3ph ranges.

Hopefully someone will chime in. There are many ro users and I have seen different minerals mentioned. Discus essential maybe?

[DJW]

Nitrification in the biofilter consumes buffer and produces acid, so you can't have a pH of 6.5 and at the same time expect the pH to stay at that point for several days. When you increase the KH to make it more stable you are also increasing the pH— they go up and down together.

As Ryan mentioned, an easy solution is to mix in some tap water for the buffer and minerals it contains. In your case though, with nitrate over 40, that's hard to manage unless the KH of your tap water is also very high.

You could go back to using the mineral additive that results in a pH of 7.3 and accept that pH as ok. I don't think there is a significant benefit to having a pH just under 7.0 as opposed to a pH just over 7.0 The main value of a low pH for discus is that low pH inhibits bacteria, but the thing is you don't really start getting the anti-bacterial conditions until the pH gets below 6. With the stocking level of your tank, you would need to change the water often, as you have discovered, or the pH might drop low enough to stall the biofilter, leading to all sorts of other problems. The biofilter runs on bacteria. Its not easy to have a biofilter full of active bacteria and at the same time have a low enough pH to suppress bacteria.

Another thing you could do is put the fish in a larger tank. Double the size of the tank and it will take twice as long for the pH to fall. Dilute the fish, so to speak.

Or you can experiment with some crushed coral in the filter. If you can find the right amount of coral, it will theoretically dissolve at the same rate the acid is being produced and buffer the acid. The rate coral dissolves is unpredictable, all you can do is try some and see what it does. I have experimented with coral but don't use it. Kyla, a member here, uses aragonite I think which is almost the same thing as coral (both are calcium carbonate) and she might be able to give an idea how much it takes.

I use all ro water and don't add any KH buffer. I change water every day to keep the fish healthy and that also keeps the pH from dropping too far. I only add KH when I won't be able to change water the next day. If I wanted to change the water twice per week I would simply add enough KH for stability and let the pH go up to wherever the buffer takes it.

[josephfu]

DJW very grateful for this explanation!

At the moment I cant get a bigger tank unfortunately. May I ask, what degree of PH swing you consider as harmful ?

For example, if PH goes down slowly by 0.8 in a 2 day period , is that harmful? and then if I change say 30% or 40% of the water, its going to go up again(maybe not by 0.8). is that sudden PH increase harmful?

Probably as you said, I would have to stick to a PH over 7 to keep things simpler if I am going to change water at 2 or 3 times a week at a 40% amount.
Not that I don't want to do 3 partial wc a week, but I always think of the possibility that something might happen and I skip a water change or 2.
(Maybe as you said then I can add some kH to compensate the drop in PH until the next water change.) Would sodium carbonate work as an emergency or sera KH+?

Crushed coral could be also a good idea as long as I find the right does according to my water changes regime.

Maybe its a bad thing , but I always like to have a plan B and plan C in things

[JamesW]

'Pure' KH is baking soda. The Arm&Hammer variety. It will increase KH and TDS but not GH. Try mixing in a teaspoon or so to your aging water change water to see what the effect is on pH. Start small and make slow small steady changes. In my opinion it is better to incorporate a modest change into your WC water and keep that constant until the tank is the same as the WC water and then take another step if you need to.

[DJW]

if PH goes down slowly by 0.8 in a 2 day period , is that harmful?

I haven't seen problems from sudden increases in pH but always have avoided sudden decreases as that is known to be stressful if done over and over. I'm not sure about the drop over 2 days, I always have lightly stocked tanks where the pH drops slower. I would lean toward playing it safe and buffer the water so the pH doesn't see-saw that much.

Would sodium carbonate work as an emergency or sera KH+?

Sodium bicarbonate (baking soda) works as a buffer to increase KH. 1 teaspoon (5g) in 50 gallons of water increases the KH by 1 degree. Better to add it to the ageing barrel not the tank. It causes a sudden rise in pH. Baking soda is very predictable but has to be added again with every water change, whereas coral stays in the tank.

[josephfu]

many thanks for the help you gave me!