Kh Gh And Ph

[JJJ]

Just like to ask a few questions on KH /PH .

GH/KH and PH work hand in hand , I am not 100% clear on how, could some one explain it? does it effect CO2/oxygen levels?

I have a 40g planted tank, recently I had ph very low < 6, I don't know why? I just finished cycling the tank ammonia 0, nitrite 0 and nitrate 20, may CO2 levels cause the effect ( I started my ferts as soon as I finished cycling)

I manage to increase PH to 7 over 2 days by raising KH, added KH powder. I just got some kh/gh kits. My reading of KH is 4 dkh (70 ppm) and my GH is 8 dkh (145 ppm) and my ph has been 7 for 3 days. My tetras have lost their appetite since, they still look ok

To maintain a stable ph you'll need high KH, what value is considered high? i am concerned my KH is a little low but if I increase it, I may increase ph as well.
the tetras are slowly geeting their appetite back

What is an ideal level of GH and KH for tetra/ pleco?
Also what is the ideal level of CO2 in a 40Ggal tank?
it is planted with 3 hygro's, 3 cypts, 1 baby tear and anbulia..

Thanks in advance

 

[waterdrop]

OK, I'll just throw a few things in and I'm sure others will answer other parts...
(you can do an advanced search on my ID with KH as the search term probably and find a lot of discussions with beginners and scientific section probably ...)

First off, to keep things simple, GH is usually just a nice thing to know, not an item you usually take action on.
KH (aka Carbonate Hardness, aka Temporary Hardness) is an important and actionable measurement. Carbonates are disolved minerals in the water that will react with acids and neutralize them to some extent - we call that "buffering." If you keep dumping in more acid then eventually the buffer will get used up and then the pH will start to drop much more rapidly from the acids. (Fishless cycling produces a lot of acids and drives both KH and pH downward.)

Each species of fish generally has a pH/KH range which they won't mind living in, as long as the pH/KH doesn't change too rapidly. They HATE rapid changes in these parameters (well, I like to think of it that way.) Its entirely likely that your tetras didn't like the *change* in KH/pH that you gave them by using the powders to raise KH/pH.

Common kitchen baking soda (not baking powder) is the cheapest, simplest way to raise KH/pH quickly and is sometimes recommended, mostly for -fishless- cycling. When you have fish, it can be too fast to raise, and it can be too fast to drop off, especially if you forget to add it, which needs frequent doing! The powders are usually like this too.

A much more accepted way (from my reading here on TFF especially) to raise KH/pH (if if must be done, which is always a question) is to use "crushed coral" (broken bits of seashells and corals that have been sorted, cleaned and packaged for LFS sale) which can be hung in a sock or put in a filter (as examples) and will very slowly and gradually raise KH/pH at a pace to the liking of fish usually. The guideline is usually to start with a very small pile in your palm, not a whole handfull, and put it in a silk bag so it doesn't mix with your other filter media in case you need to remove it later. It will take a week or two usually to see much effect. After that you increase or decrease the amount needed gradually based on your test readings.

OK, that's my bit to which others will hopefully add... I've read at least one account where someone set out to raise KH because of worrying that CO2 would drop pH too low but then later decided that KH raising was not needed really for that. I didn't fully understand what the issues were there so perhaps there are some other considerations that one needs to take for the planted tank with CO2. I know that many plants and tetras are supposed to really like being in acid water, so the issues seem somewhat complicated in reaching the ideal.

~~waterdrop~~