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pH and KH problems in African Cichlid Aquarium

Updated 9-18-13

This article is a simple question and answer post between myself and two customers.


One of these days I'm going to write down the chemistry for pH, kH and GH and maybe I will remember it, eventually. But for now I new some advice. I got many good suggestions on my fairly new mbuna tank and thus far it has been going very well but something is amiss with my water.
My tap water comes out at about 7.6 pH. I have about 30 pounds of holey rock in there currently. But, for some reason my pH seems to be dropping. Currently it is approaching 7.2

My gH is still pretty high 200 or so, but my kH has also started dropping from around 120 to currently just under 80. Nitrates are between 10 and 20. 0-0 on the bad stuff.
I am doing 30-40% weekly water changes. I have 16 fishes in a 55 gal between 1 1/2 and 3".
I may need yet another reminder about water chemistry or could it be my 'mystery' substrate. Along with some small tan gravel which I have used in many tanks with no apparent detriment, I also have maybe 15 # of stuff that was given to me a while back along with my first cichlids, a little tank etc. I have no idea what it is but she mentioned it was "supposed to be good for aquarium plants".
It is approximately 1/3 each of black, brick red and tan stone. Though relatively small they are more like little chips than rounded pebbles - fairly jagged and rough on the edges. Then again it may not be this at all.
Any ideas?
Thank you.


There's probably something producing a heavier than normal amount of acid. The normal biological process of Nitrification will have the same effect as titrating with nitric acid (NHO3). Carbonate hardness (KH) is slowly used up in this process, reducing buffering and pH. When the KH is completely depleted, you will find that the aquarium pH will stabilize around 4.4 (of coarse this is much to low), and if you have a large amount of organic build up, it could be part of your reason (although your Nitrates are stable and low from what I read).

More information about Nitrogen Cycle:
*The Aquarium Nitrogen Cycle
*Aquarium Nitrates

Eheim Battery Aquarium VacuumWhat are your filter(s)? Some filters such as large canister filters can become what is referred to as “Nitrate factories”. In this process, KH (Carbonate Hardness) is deplete if not cleaned (rinsed) regularly.

If you have an Under Gravel filter, make sure you occasionally remove the lift tubes and siphon out the mulm that accumulates under the plate.
With all filters, it's still important to remove as much mulm and other organic debris as possible.
An Aquarium Vacuum is the preferred method for both water change and mulm removal; although in between water changes an Ehiem Sludge Remover Vacuum is an excellent tool to have, especially in high bio load aquariums.

Product Reference Link: Aquarium Vacuums

As for your KH & GH, I'm a big proponent of keeping an adequate KH (minimum 150 to 300 KH) and Calcium level (part of GH) for many reasons.
One of them is for the problem you are having and the other is that GH is simple way of knowing your calcium levels in fresh water. It's also very important to fish health.
Crushed coral or aragonite can help, but in my experience (especially in High ph aquariums such as African Cichlid tanks), they are not always adequate as these substrates do not dissolve fast enough to release the proper amounts of Bicarbonates, Magnesium, or Calcium for KH and GH.

In the closed environment such as an aquarium, I found that outside sources that are manually added and dissolve, are often necessary.
There are many products available from SeaChem Malawi Buffer which is preferable to baking soda due to the balance of sodium bicarbonate magnesium and other minor elements; to the Wonder Shells which provide essential positive mineral ions (cations) necessary for fish osmoregulation.

How to Fish Drink; Osmoregulation

Product References:
*SeaChem Malawi Buffer
*AAP Wonder Shells

At the risk of being too commercial, my personal and more importantly my aquarium maintenance clients aquariums (especially Rift Lake Cichlids) are rarely without a regular Wonder Shell for Calcium and electrolytes control.

As for the plant substrate you were given, this sounds like a product such as Eco Complete or SeaChem Flourite which can lower your pH.

I have an detailed article about KH, Calcium and electrolytes:
The Importance of Maintaining Healthy Calcium Ion levels, GH, pH, and KH levels

My point in mentioning GH is that Calcium and Magnesium are part of GH and are both necessary for proper osmotic processes in fish.
If there are problems with KH, many times there are problems with GH (although in this case there does not seem to be a problem).
The problem here indicates too much organic decomposition thus reducing the KH. Again I would check filters for build up too. When I called on customers aquariums experiencing this problem, many times they had a filter with a thick layer of mulch on the bottom.
Removing this, then adding a KH stabilizer (which I had better results with a slow dissolving KH stabilizer), and the problem was solved.

See also:


Carl, I am curious how the Wonder Shells compare per use with SeaChem Or Kent?
I am definitely on a budget so sometimes I use 'good' at a Lower price, rather than 'better' at a higher price.
Does crushed coral, holey, aragonite, etc. buffer the water by actually dissolving, exchanging ions or whatever, into the water or is there some sort of chemical reaction in the water which eventually dissipates?
How does the coral+ 'wear out' and have to be replaced?
I appreciate ya

For freshwater aquariums my experience has been equal to SeaChem (I have had better results with SeaChem products over Kent Marine and use them 10/1 over Kent for marine aquaria). For marine aquariums the Wonder shell help, but the well balanced SeaChem line is hard to beat (such their calcium polyglucanate)
The Large wonder shells are only a about $2.50 and are hard to beat for Freshwater.

My understanding is the same as using a cave chemistry analogy;
Water containing acids such as carbonic or nitric acid, VERY slowly dissolve away the minerals in the crushed coral, etc. which is why I have found in freshwater and marine, that the rate of dissolving does not keep up with buffer depletion.
Basically the coral does not wear out, rather dissolves away.

Recommended Related articles:
*Maintenance of a Balanced Aquarium Redox Potential

*Aquarium Medications; How they work

For more aquarium information articles:

*Aquarium & Pond Information

Recommended/Useful Aquarium Products:

*Ultraviolet Sterilizer- for disease prevention, improved Redox balance
*Replacement UV Bulbs- these are important to change every 6 months to keep your UV Sterilizer functioning properly


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In Chronological order of writing with the newest at the top

  1. How to Treat Sick Fish
  2. Whirling Disease in Fish
  3. Reef Aquarium Chemistry Maintenance
  4. Use of RO, DI, Softwater in Aquariums
  5. Lighting Theory of a Planted Aquarium- RQE, PFY, PAS, & PUR
  6. Aquarium or Pond Bio Load
  7. Tuberculosis in Fish
  8. PUR vs PAR in Aquarium Lighting
  9. Head Pressure in Aquarium and Pond Water Pumps
  10. Fin/Tail Rot For Betta & ALL Fish
  11. Angelfish Virus/Aids
  12. Activated Carbon
  13. Fish Baths/Dips as an aid to treatment
  14. Streptococcus gram positive bacterium in aquariums, Eye Infections
  15. Hydrogen Sulfide
    production in anaerobic De-Nitrification for Aquarium/Ponds
  16. Fish Shipping
  17. Aquarium Size, Fish Stunting
  18. Aquarium Algae,
    BBA & Brown Algae in particular
  19. Aquarium Salt (Sodium chloride) in Freshwater Aquariums
  20. Betta Habitat; Wild Bettas to Domestic Betta environment parameters
  21. HITH; Hole in the Head Disease
  22. Aquarium Protein Skimmers, Ozonizers
  23. Power Head/ Water Pump Review
  24. Molly Disease/ Mollies in an Aquarium
  25. Basic Fish Anatomy, Fin Identification
  26. Aquarium Moving/ Power Failures
  27. Octopus as Aquarium Pets
  28. Aquarium Nitrates
  29. Ichthyophonus protists, fungus in fish
  30. Aquarium and Pond Filter Media
    Types; Mechanical, Bio, Chemical
  31. Aquarium Water Conditioners (also Pond)
  32. Fish Parasites; Trematodes & Monogeneans; Annelids and Nematodes;
    Flukes, internal worms, Detritus Worms (often confused with Planaria), Micro Worms
  33. Aquarium Silicone Application;
    DIY Aquarium Repair & Glass thickness
  34. Pond Veggie Filters; DIY Bog Filter
  35. The difference between Plaster of Paris and Aquarium Products such a Wonder Shells:
    Identification, prevention & Treatment
  37. AQUARIUM TEST KITS; Use & Importance
  38. SEXING FISH; Basics
  39. Chocolate Chip, Knobby and Fromia Starfish
  40. Freshwater Velvet & Costia
  41. Usnic Acid as a Fish Remedy
  42. Aquarium Heaters; Types, information
  43. The Lateral Line in Fish, Lateral Line Disease
    or Head and Lateral Line Erosion (HLLE)
  44. Tap Water use in Aquarium; Chloramines, Chlorine
  45. Can Black Ghost Knife fish give an electric shock?
  46. Bio Wheel Review; Do Bio-Wheels really work?
  47. How do Fish Drink?
    Use of RO Water
  48. Cyclops, and Predatory Damselfly larvae
  49. Betta with Dropsy;
    Treatment and Prevention of DROPSY in all fish
  50. pH and KH problems in African Cichlid Aquarium
  51. Aquarium Gravel, which size?
  52. Blue green algae, Cyanobacteria in Ponds/Aquariums

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