GH, KH & pH: Research & Sources

What this research record covers

The Tank Guide assembled one master research package on GH, KH and pH in freshwater aquariums (compiled August 2026). It is a 94-page reference compilation, not an article. Its core idea: each parameter answers a different question — pH is how acidic the water is right now, GH is how much calcium and magnesium is dissolved, and KH is how much acid the water can absorb before pH moves. The package covers:

• What pH measuresThe logarithmic scale, how pH is measured, and why it swings over a day.
• General hardness (GH)Calcium and magnesium, units, and their roles in fish and invertebrates.
• Carbonate hardness (KH) / alkalinityTerminology, units, and how KH is used up and replenished.
• How GH, KH and pH relateCommon water profiles and why one number doesn’t predict the others.
• Buffering and pH stabilityLow-KH systems, and a look at “stable pH matters more than the right pH” and “don’t chase pH.”
• Soft-water and hard-water fishSpecies requirements, osmoregulation, and survival vs. thriving vs. breeding.
• Source waterTap, well, softened and blended water.
• RO/DI water and remineralizationWhy pure RO water isn’t aquarium water on its own.
• Adjusting GH, KH and pHMethods, dosing arithmetic and risks — including driftwood, botanicals, crushed coral and aquasoils.
• Planted tanks and CO₂The limitations of the common pH/KH/CO₂ table.
• Nitrification and Old Tank SyndromeHow the nitrogen cycle consumes alkalinity, and gradual pH decline in older tanks.
• Testing, units and conversionsIncluding TDS and conductivity.
• Shrimp, snails and plantsIncluding where common shrimp parameter targets are hobby convention.
• Care-sheet ranges, acclimation and mythsWhere commonly repeated numbers and claims come from, and how well they hold up.

This is a summary of the package’s scope. It is not a new set of care recommendations — for practical guidance, read the articles below.

Tank Guide content developed from this research

These pieces were developed using this research package.

• Article

  GH, KH & pH in Your Aquarium: What They Actually Tell You

  What GH, KH and pH each measure, how they relate, and why the numbers don’t move together.

• Article

  How to Raise or Lower GH, KH, and pH in Your Aquarium (Without Making Things Worse)

  Methods for raising or lowering each parameter, and when adjusting is — or isn’t — worth it.

• Article

  Hard Water vs. Soft Water: Does Your Livestock Actually Need Something Different?

  Whether your fish, shrimp and snails actually need different water, and how much it matters.

• Podcast episode · Tank Guide Life

  Confused by GH, KH, or pH? Listen Before You Adjust — listen on Spotify (opens in a new tab)

  A Tank Guide Life episode on reading GH, KH and pH before reaching for an additive. Opens on Spotify.

Production relationships were confirmed by the creator of The Tank Guide.

Evidence at a glance

Every bibliography source was checked on its own, and every link between a source and a statement in the package was reviewed separately.

How to read this research record

Direct support

The source directly supports the specific statement attributed to it.

Partial support

The source supports part of the statement, but the package wording is broader.

Background support

The source is relevant context but is not direct proof of the full claim.

Manufacturer documentation

The source verifies what a manufacturer says about its own product. It is not independent scientific validation.

Bibliography-only

The historical package listed the source but did not clearly connect it to a specific statement.

Historical attribution limited

The relationship was reviewed, but the surviving information is not sufficient for stronger attribution.

Citation mismatch

The cited source does not support the claim attributed to it.

Each source also carries a verification label: Verified; Verified · citation corrected (the source was confirmed, but details such as authors, journal, year or URL needed correcting); Verified · limited scope; or Could not be independently verified.

Source library

All 43 sources from the package bibliography, grouped the way the original package grouped them by type of evidence. Each entry also shows its audited source type and verification result. Open a group to see its sources; links go to the verified source and open in a new tab.

Important limitations

The audit is complete, but it did not resolve everything. These are the gaps that remain.

1. Four bibliography sources could not be independently verified

   • Carbon dioxide (Tucker, C. S., 1984)
   • Accuracy of pH/KH relation for CO₂ (discussion thread)
   • pH relationship and the KH on a chart
   • Specialist shrimp-keeping resources (unnamed group)

   Tucker (1984) is cited in the verified SRAC Publication No. 464, which supports that it exists, but the original 1984 publication was not located. The two forum threads could not be recovered, and the shrimp-keeping resources were never named individually in the package.

2. Timmons et al. (2018), Recirculating Aquaculture, was verified with a scope limitation

   The book’s bibliographic identity was verified, but the exact 4th-edition passage used for the nitrification stoichiometry (how much alkalinity nitrification consumes) was not directly inspected. The same figures are corroborated by the wastewater and aquaculture sources in this record, but this particular book-to-claim link is not treated as fully verified.

3. Wurts (2002) does not support one claim attributed to it

   The package cited Alkalinity and Hardness in Production Ponds for a claim that swings in alkalinity may disturb hormonal regulation, gonad development and gamete production. Independent verification found that this article does not contain that reproductive mechanism. It discusses alkalinity, hardness, pH swings, stress, growth and pond productivity instead.

   The historical citation is preserved, but this specific claim should not be treated as externally supported by Wurts 2002. No replacement source has been substituted.

4. The peat / atomic-absorption claim remains unresolved

   The package described an observation that peat-filtered water tests softer on a hardness titration while calcium measured by atomic absorption stays unchanged. That observation came from a hobby forum thread that could not be recovered, and it has not been traced to a peer-reviewed source. It should not be read as established evidence.

5. Shrimp parameter ranges cannot be independently audited

   The package compared commonly cited shrimp GH, KH, pH and TDS ranges using an unnamed group of specialist shrimp-keeping resources. The individual sources did not survive in the package, so that numerical comparison cannot be checked. The package itself labelled these targets as hobby convention.

6. Manufacturer documentation is not independent testing

   The Seachem Equilibrium and SaltyShrimp Bee Shrimp Mineral GH+ pages were verified as the manufacturers’ own documentation. That confirms what each company says about its product, including dosing figures — not that those claims were independently tested.

More broadly: not every source is peer-reviewed aquarium research. Much of the physiology research studies wild or model species, and aquaculture and wastewater figures come from ponds and treatment plants rather than glass tanks.

What we did not do

• We did not silently rewrite historical citations. The original package wording is preserved alongside every correction.
• We did not replace missing sources with convenient modern substitutes.
• We corrected source details (authors, journals, years, URLs) in our research registry while keeping a record of what the original package said.
• We did not upgrade a source’s standing just because it was on the right topic.
• We did not hide unavailable references — they remain listed and marked as unavailable.

How this record was built

1. The Tank Guide assembled a master GH/KH/pH research package for content development.
2. The package’s bibliography was extracted into The Tank Guide’s research registry — 43 sources and 68 source-to-claim relationships.
3. Every bibliography source received an independent verification result.
4. Source-to-claim relationships were reviewed separately from the package’s own evidence labels.
5. Corrections and unresolved citations were preserved rather than hidden.
6. The audit was completed on September 25, 2026.

The Tank Guide did not conduct the external scientific studies listed here. FishKeepingLifeCo, publisher of The Tank Guide, compiled, reviewed and organized the research; the studies and references belong to their respective authors and publishers.