KH, PH, Co2, substrates, fish and plants ! - The Planted Tank Forum
LinkBack Thread Tools Display Modes
post #1 of 5 (permalink) Old 04-07-2016, 11:23 AM Thread Starter
Algae Grower
PTrader: (0/0%)
Join Date: Mar 2013
Location: Bristol, UK
Posts: 88
KH, PH, Co2, substrates, fish and plants !


My tap water is PH 8.2 / KH 11 / GH 13. I have been reading that high KH values reduce the waters ability to absorb Co2, and this is reflected in those PH/KH/Co2 charts.

The general advice seems to be to not 'fight' the parameters of your tap water as this often results in unstable conditions, and the better approach is to stick with your tap water and choose plants and fish which like those parameters.

Based on the above, and the fact that I will be injecting pressurised Co2 in to my tank, is it a good idea to use a 'complete' substrate such as ADA Amazonia which will lower PH & KH?

My understanding is that this could be good because it will increase the waters ability to absorb Co2, and ammonia will be in a less toxic form, but it is still altering my tap water which goes against the general advice I have read. What confuses me even further is that when I do a 50% WC with my tap water, the chemistry will be different from what is in the tank because of the substrates influence, and surely this will be causing those unstable conditions that I was supposed to be avoiding.

So in summary my questions are:

1. Should I chose an inert substrate, or one which will lower KH & PH.

2. Should I be looking to lower my KH and PH values for better Co2 absorbency and less toxic ammonia, which in turn will allow me to keep some species that I desire which prefer slightly softer water....
OR should I be choosing fish and plants for my harder tap water and just accepting that Co2 absorbency will be more difficult and more toxic ammonia could exist ?

Sorry for the length of the post, I would appreciate any advice to resolve these conflicts in my thinking.

Many thanks

paul195 is offline  
Sponsored Links
post #2 of 5 (permalink) Old 04-07-2016, 12:25 PM
Planted Member
maxhrbal's Avatar
PTrader: (0/0%)
Join Date: Mar 2016
Location: NW Pennsylvania
Posts: 165
I have a planted tank with inert sand and my municipal water is about the same but I have a water softener. As for the ph, in my (relatively short) experience, my aquarium naturally lowers the ph. Still trying to figure out what causes this. I'm believe driftwood helps absorb minerals and lowers kh/gh but I think it would be a slow process not to be relied on. I agree, I wouldn't try to fight your tap water parameters too much but your hardness does seem a bit high. I haven't experimented with special substrates, but maybe experiment with a smaller tank before deciding.

Sorry I had no direct answers to your questions. LOL.

Oh...might be the reason why my ph lowers naturally, but the carbonates and other minerals in hard water are excellent ph buffers, which might not allow your ph to go much lower as it does in my tank. (<5 kh/gh)


Oh, your ph most likely cannot be lowered without your kh and gh being lower. Hard water is a great ph buffer which means you could add sulfuric acid to your tank and it would almost immediately be neutralized by the minerals in the water and the ph would just jump right back up to around 8 or so.


Last edited by Darkblade48; 04-08-2016 at 03:20 AM. Reason: Please use the edit function for back to back posts
maxhrbal is offline  
post #3 of 5 (permalink) Old 04-07-2016, 12:53 PM
Planted Tank Obsessed
PTrader: (6/100%)
Join Date: Jul 2015
Location: South Florida
Posts: 346
Don't mess with tap values. If your doing 50 percent changes on a weekly basis the substrate will not alter your kh drastically, to my understanding.
I use inert substrate and r/o water. The soft water species I grow cannot tolerate my hard tap water.
Mikevwall is offline  
post #4 of 5 (permalink) Old 04-07-2016, 01:07 PM
Planted Tank Guru
PTrader: (0/0%)
Join Date: Jan 2010
Location: Contra Costa CA
Posts: 11,721
You can set up the tank (and mess with the water) all you want. Just get the recipe figured out and stick to it.

What kind of fish do you want? Research the fish needs. GH, pH, TDS, other (black water species?)
Get a gallon of RO water. Make several blends. See which comes closest without going over.

Here is how I do this:
1) Make the GH suit the fish. You can keep hard water fish that like your water, or you can blend RO + tap until you make a good GH level for whatever livestock you want.
2) Make the KH equal the GH. KH stabilizes the pH. In general a high KH means high pH. A low KH allows something else to control the pH. For example, when ADA substrates remove the KH this allows CO2 and decomposing organic matter make the pH more acidic. Check the pH requirement of the fish (most will thrive at a wide range of values) and adjust the KH to keep the pH in that range.
3) A black water species would have peat moss in the water prep barrel.

ADA substrates will remove carbonates. Also, these materials add ammonia to the tank. When you first set up the system you will find the KH drops to 0 degrees very fast and the ammonia climbs. The ammonia is good for growing nitrifying bacteria, but the low-to-no KH is bad. To get the system through its first month, and grow the nitrifying bacteria, you will be doing water changes (to keep the ammonia and nitrite under 5ppm). I would do this with tap water, not tap + RO. This will give the bacteria the minerals they need.
Diana is offline  
post #5 of 5 (permalink) Old 04-08-2016, 11:22 AM
Wannabe Guru
PTrader: (1/100%)
Join Date: Mar 2011
Location: College Station, TX
Posts: 1,049
The absolute easiest way to correct whacky tap water values is to blend it with RODI water until you find the perfect set and remember your blend. Easy as that. For me my tap water comes out at 24 dKH and zero (yes zero) dGH. When I water change, it's 4 buckets of RODI, 2 buckets of tap, and 2 tbsp of GLA GH booster. Gives me perfectly stable and balanced 6 dKH and 6 dGH water.

Sent from my iPhone using Tapatalk

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
bpb is offline  


Quick Reply

Register Now

In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome