The Defin­i­tive Guide to Water Para­me­ters in Plant­ed Tanks [Full Explanation]

Today I’m going to show you exact­ly how to take con­trol of your tank’s water, reduce algae, boost your plant growth, and hon­est­ly… just give you a few less things to wor­ry about—at least for your tanks.

I’ve worked with water para­me­ters in one way or anoth­er for near­ly 10 years — below is the knowl­edge and spe­cif­ic meth­ods I reg­u­lar­ly use to get opti­mal and safe para­me­ters in my plant­ed tanks.

Let’s dive in:

• Why do these para­me­ters mat­ter at all?
• The eas­i­est way to measure
• water changes mat­ter — a lot
• Gen­er­al Hard­ness (GH)
• Car­bon­ate Hard­ness (KH)
• pH and a few myths

Why do these para­me­ters mat­ter at all?

Water para­me­ters are impor­tant. More clear­ly put:

Water para­me­ters will make or break your tank, hands down.

Oth­er fac­tors like CO2 usage and fer­til­iza­tion pale in com­par­i­son to the effect bad water para­me­ters can have on your plant growth.

If your GH is low (or 0), you’ll have poor (or zero) plant growth, algae issues, and like­ly unhealthy live­stock. Shrimp and oth­er inver­te­brates will like­ly die in your tank.

If your KH is (unin­ten­tion­al­ly) sky-high, your live­stock will also suf­fer, and plant growth will be sig­nif­i­cant­ly stunt­ed and slow.

If your pH is out­side the ​‘stan­dard’ 6.5−7.5 range, your plants will tech­ni­cal­ly grow—but it’ll be slow, and like­ly stunt­ed. Live­stock will also suffer.

Hope­ful­ly that got your attention.

This stuff mat­ters, not just for beau­ti­ful plant growth, but for prop­er care of live­stock. Suf­fer­ing is nev­er a good thing for your fish.

The eas­i­est way to measure

There are a few dif­fer­ent meth­ods to mea­sure your water parameters.

Not all meth­ods are equal. Test strips are extreme­ly unre­li­able, and essen­tial­ly unus­able for those that aren’t able to eas­i­ly dif­fer­en­ti­ate between some­times-slight col­or differences.

Reagent test kits are almost always the best choice for most aquas­cap­ers. There are dig­i­tal meters avail­able (I use Han­na meters), but the price is not begin­ner-friend­ly, and it’s impor­tant to know: you don’t need fan­cy test­ing meth­ods to ​‘get it right’.

For bud­get mind­ed indi­vid­u­als, I’d rec­om­mend a prop­er reagent test kit—the API kits are plen­ty accu­rate for our needs as aquascapers:

Water Changes Mat­ter — more than you think

Most peo­ple don’t con­sid­er how water changes affect your para­me­ters beyond the usu­al ​“leave water out for 24 hours” (which is false), or ​“water change when need­ed” (which is also false, in most cases).

Water changes can mean the dif­fer­ence between ​“easy main­te­nance” and ​“noth­ing is ever sta­ble” in your plant­ed tank.

In gen­er­al:

• 30% water changes, three times a week. 
  
• RODI water if at all pos­si­ble (it’s cheap­er these days than it’s ever been)
• Agi­tate sub­strate and plant sur­faces to remove organ­ic waste

You’re prob­a­bly think­ing, ​“30% three times a week is INSANE”. 

It’s not — you’re spend­ing that time on some­thing, whether it’s water changes, or pur­chas­es you make try­ing to fig­ure out why your para­me­ters aren’t right, or troubleshooting/​testing to diag­nose algae buildup issues.

Even if you ignore every­thing else in this arti­cle, remem­ber this:

RODI water is the fastest way to a crys­tal-clear, headache-free tank.

Gen­er­al Hardness

GH is an ini­tial­ism (‘abbre­vi­a­tion’, essen­tial­ly) of Gen­er­al Hard­ness. You might also see terms like ​‘Total Hard­ness’, ​‘ºGH’, or just ​‘GH’. They all refer to the same thing: GH is a mea­sure­ment of the cal­ci­um and mag­ne­sium present in your water.

When some­one says ​“hard” or ​“soft” water, they’re refer­ring to how much cal­ci­um and mag­ne­sium is present — the GH val­ue.

Impor­tant:GHdoes not have to equal KH. In nature they’re often equal, but in our tanks these val­ues can absolute­ly be different.

GH is essen­tial­ly an ​“offi­cial” way to mea­sure how much cal­ci­um and mag­ne­sium you have in your water, and you’ll want to know that — here’s why:

Cal­ci­um and mag­ne­sium are macro nutri­ents that are required for lush, opti­mal plant growth.

If your GH val­ue is low, cal­ci­um and mag­ne­sium will be the lim­it­ing fac­tor for plant growth in your tank, you’ll like­ly run into algae issues as you increase your light lev­el and CO2. (More on that here.)

High GH/KH val­ues are impor­tant for hard­wa­ter fish like cer­tain Cich­lids — and the reverse is true for dis­cus, which thrive in soft­wa­ter with low­er GH/KH values.

Aim for a GH val­ue of 4 – 7 in your plant­ed tank. You’ll know if your tank is an excep­tion to this range. (i.e. you’re doing a black­wa­ter tank, or a dis­cus biotope, for example.)

Car­bon­ate Hardness

You’ll prob­a­bly see the term ​“KH” in the aquar­i­um world — that’s car­bon­ate hard­ness. It’s a mea­sure of the car­bon­ates and bicar­bon­ates in your water.

For our pur­pos­es as aquas­cap­ers, it has zero effect on most plants. Its sole pur­pose is sta­bi­liz­ing the pH val­ue of your water.

For most aquar­i­ums, main­tain­ing a KH of 3 is optimal.

Some trop­i­cal species of plants and live­stock thrive in low­er KH val­ues, but these are excep­tions to the above principle.

There’s one thing about KH I want you to remember:

KH changes can dra­mat­i­cal­ly affect livestock.

Fish and shrimp main­tain their cell struc­ture through a process called osmoreg­u­la­tion, and sud­den KH changes are extreme­ly tax­ing to their health, whether KH is increas­ing or decreas­ing. As a result, I’d high­ly rec­om­mend test­ing your tap water (or RO water, if you’re able) to deter­mine whether you need to mod­i­fy your KH, and stick to it.

If you have live­stock, prop­er care means ensur­ing your KH val­ue is sta­ble. Allow­ing this to sig­nif­i­cant­ly fluc­tu­ate is extreme­ly stress­ful on fish and many invertebrates.

pH and the ​‘swing’ myth

pH is essen­tial­ly a mea­sure of the hydro­gen present in your water. It’s more com­pli­cat­ed than that, but for our needs as aquas­cap­ers that’s enough.

Neu­tral water has a pH of 7, acidic water is low­er than 7, basic water is high­er than 7.

For aquas­cap­ers, a pH of 6.5−7.5 is the ​“ide­al” range for near­ly all live­stock and plants. There are occa­sion­al excep­tions on both sides (very-low / very-high pH biotopes, for exam­ple), but you’ll know if you have one of these exceptions.

You might see forum post­ings and arti­cles online about reduc­ing pH swing in your tank — with­in rea­son, this isn’t necessary.

Sig­nif­i­cant pH swings hap­pen in nature, and are a nat­ur­al part of the envi­ron­ment for near­ly all fresh­wa­ter live­stock. If you’re curi­ous, Den­nis Wong has a great in-depth arti­cle on pH here where he goes into the details about what that looks like in var­i­ous biotopes.

This para­me­ter does mat­ter, but don’t stress about any­thing less than a 1 – 2 pH swing over the course of a day.

Your Turn

What’s your expe­ri­ence with water para­me­ters? Got a tip for chang­ing water? Tell me in the comments!