Low KH?

Greetings All--

I had a 15 gal setup from November until July this summer, until rampant heat waves killed all of my fish. My tank was freshwater, plastic plants, black gravel at the time. Now we are in September, and I decided to go DIRT. Currently dirted tank using Organic Choice potting mix, layered with red clay and oyster shell. Capped with black gravel re-used from old set up. In the old set up, I always had LOW KH. Even with some sea shells, never could seem to raisethe KH and my PH was always between 6.0 and 6.5. Now that I have had the new set up, with oyster shell mixed in the soil and all--I still have low KH. I have a few young plants in the current set up, as well as some driftwood, but no fauna (this has been only running 1 week). I am still a newbie, I still am not completely sure what KH will do in my tank overall. My PH is about 6.3. KH 0. HELP! Please explain (somebody, anybody) what is the importance of KH in the planted tank, and how can I stabilize in my tank. I am trying a "Walstad, El Natural" method here..... so no CO2 injection. And I have not "dosed" my tank with anything either. HELP!

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Comment by Robert Jango on September 13, 2012 at 12:22am: KH is carbonate hardness and it is raised with the addition of calcium and magnesium. A high KH stabilizes your PH, but it sounds to me like your PH is already very stable. You said it always measures around 6.3. So what's wrong with that? Most tropical fish hobbyists would kill for soft water and PH between 6 and 6.5. I set up a rainwater collection system just for that purpose. Many of our most desirable fish love these conditions.

You can fool with the chemistry of the water but what about water changes? Your going to have to treat the new water as well as the water already in the tank. Sounds to me like you already have a tank that most fish and plants will love.

Comment by thebklynblujay on September 13, 2012 at 2:30pm: Ah! Thanks so much! I assumed a KH of 0 was bad; that this would mean my plants won't be getting the proper minerals needed to flourish. So I see, I'm just being a worried parent unnecessarily.... Again thanks!

Comment by Robert Jango on September 13, 2012 at 9:03pm: Yeah the natural soil and clay will provide the plants with plenty of nutrition. And if you let the fish poop settle, your clay and soil will absorb it and keep the substrate fertile forever.

Comment by thebklynblujay on September 13, 2012 at 11:31pm: Thanks so much Mr Jango. Next step: stocking suggestions.... tank is small, plants are young. Wisteria, Anubias nana, Java fern and Java Wendelov, along with a struggling Red Temple plant. Thinking of small, hardy schooling fish. Bloodfin tetras? How soon? I was wondering, should i wait til plants grow out more, or would adding fish sooner actually help plants grow better? I really appreciate, kind sir!

Comment by Robert Jango on September 14, 2012 at 12:35am: You can stock them right away, but change the about half the water every week until you get the plants and bacteria going. Once they're established they'll suck up all the ammonia and nitrogenous waste that come from fish poop, uneaten food, and other waste. And yes - adding the fish right away will help the plants and vice-versa. After a couple of months you can change the half water once every 2-3 weeks or once a month if you have a lot of plants in the tank or floating plants. You mention Diana Walstad. Did you know that she changes her water about once a year or in some cases never? She really understands the relationship between plants and fish. But to be on the safe side change your water about once a month.

Stocking suggestions? Obviously you want to avoid an Arapaima - its gets 9 feet long. Cichlids are generally territorial but some are ok when they're not breeding. This is really the fun part of the hobby. Get whatever strikes your fancy but research them before placing them in your tank. In a worst case scenario you can always return an undesirable fish for store credit.