Should I be worried about low kH in new tank?

TPIRman

TPIRman

Fishkeeping Yellow Belt
Mar 5, 2004
232
0
16
New York, NY
Visit site
Hi all,

I have a 10-gal. tank stocked with 7 danios that has been running for about three weeks now. My fish look pretty happy -- active, breathing properly, eating well, etc. -- but I consistently get "alkalinity" readings at or near zero on my test kit. The pH has remained constant at about 6.6-6.8 -- hard to tell exactly with those darn test strips! Once the tank is well-established, I would like to add peat extracts (a.k.a. Sera Morena "blackwater conditioner") and a piece of bogwood to make the tank a more natural habitat for the fish. Before that (in about a week, actually), I plan to add live plants. I'm worried that the low kH means that I am setting my fish up for an unpleasant pH crash, so before I make any changes to the tank, I'd like to be confident that they will be safe.

However, I don't just want to throw a bag of crushed coral in the tank without really knowing the consequences. I've read up on the effects, especially ArkyLady's tests, and while I like the increase in kH, I don't want to raise my pH too much. 6.8 is right where I want it to be.

So I guess my question is, can/should I increase kH to "safeguard" my tank against a pH crash without raising the pH significantly? Or, do I even have cause to be worried?

Here are my full tank details so you have the complete picture.

- 10-gal. tank
- Penguin "Micro Bio-Wheel" Filter (100 gal/hr)
- Tetra AP30 air pump (30 l/hr) feeding 14" "bubble wall"

Water Chemistry:
- pH: ~6.8
- Ammonia: 0.25 ppm
- Nitrates: 10 ppm
- Nitrites: 0 ppm
- gH: ~50 ppm
- kH: ~0 ppm
- Temperature: 76° F

I am doing 50-60% water changes daily to keep ammonia levels down.


Thanks in advance for any advice you can give!
 
If your KH is really 0, your pH will not stay at 6.8. It'll crash at some point: bad bad bad.

Try a tablespoon or two of crushed coral in your filter. Its slow-acting and long-lasting. Keep an eye on it for a week or so, tweek it to get a pH/KH balance you're happy with. Very manageable.

A pH crash is a sure recipe for dead fish and running a low KH is good recipe for a crash. Ideally you want to keep up above 3 dKH or so. You should be able to stay slightly acidic at that level.
 
Thanks for your reply! A quick follow-up question:

- Say down the line, the crushed coral has taken effect and raised the kH of my tank, and also raised the pH along with it -- let's say to 7.2 for argument's sake. Then I make a water change with water from the tap, which has a pH of about 6.8. Will this be harmful to the fish? Will I have to start using additives every time I make a water change to match the new water's pH to that of the tank water?
 
Bounces are bad as a general rule and should be avoided, but water isn't a rock-solid sort of thing… its fluid. Things change. Without an adequate buffer they can change fast and a lot.

Lots of Co2 supplementing planted tank folk take small daily pH waves for granted: the pH is lower at night when the plants stop photosynthesizing. This happens in nature and is a normal type thing. But thats small waves, not big spikes. Lets say your water is generally around 6.7 and with the coral you boost it up to 6.8 (or even 6.9) — a 50% water change might momentarily drop your tank as much as a tenth or so before the equilibrium swings back in. This isn't the type of thing thats going to hurt the fish.

The crushed coral is there to act as a safety net. Its supplementing the buffer. You don't need a whole lot. Add a tablespoon. Keep an eye on things and see where you are after a week or so. Maybe add a little bit or take a bit out. You don't really need to be swinging your pH around with this and you don't want to be fiddling with it at every water change. As the buffer gets used up, it gets replenished. Every few months you might dump the old and put in a fresh tablespoon.

I have very soft and acidic water (negligible KH, pH in the low 6s) and a CO2 tank… and a mesh bag of crushed coral in the filter. It works. No trouble with fairly large water changes on a regular basis…

HTH
 
Last edited:
Thank you for all your help, carpguy! I picked up a little baggie of crushed coral at the LFS (they gave it to me for free) today. Now I just have to find the appropriate mesh bag -- maybe my girlfriend has some old pantyhose...

Thanks again.
 
Update

Hi, carpguy et al.,

I wanted to update you on my progress. I tied up 1 tbsp. of crushed coral in the toe of some old pantyhose and dropped it into the filter about a week and a half ago (specifically, 3/11). I checked my kH today (3/20), and it remains at essentially zero, or at least barely detectable and the same as my tap water. In the time that has passed, I have made four water changes of approximately 50% each.

I'm wondering what my next step should be -- add more crushed coral, or wait? Is placement in the filter a factor? I just dropped it to the bottom. My filter is not very large, so there's not really room to hang it.

I added a few small plants (see tank specs) recently, too -- would these be holding my kH down? Or the water changes?

I got a good package deal on Flourish fertilizers from my LFS (Flourish, Flourish Excel, and the NPKs), but I'm wondering if I should hold off on using them until the kH is in a better place.

The tank is fully cycled now, so kH is my last major water-chemistry concern. Sorry for the litany of questions. I really appreciate all the guidance you've given.

Edit: Today I'm wondering also if the pantyhose might be too tight a mesh for much carbonate to leach out. Is thiss possible, and would it be safe just to put the tablespoon of crushed coral directly in the filter box?
 
Last edited:
You must log in or register to reply here.
AquariaCentral.com
Top Bottom