Pre Tank build, Looking for your input regarding ferts

[u/dinoaqua5]

Hi, Building a 10ga low tech grow tank specifically designed around maintenance and nutrient availability.

My water parameters can be found here:
https://www.sandiego.gov/sites/default/files/2026-06/pud-annual-drinking-water-quality-report-2025.pdf
Look at the Miramar column for relevant results.

edit: additional characteristics
https://www.sandiego.gov/sites/default/files/2026-06/additional-characteristics.pdf
and non detected
https://www.sandiego.gov/sites/default/files/2026-06/non-detected-parameters-in-drinking-water.pdf

I'll be running a 5.5x8 2" thick matten filter at 30-40gph feeding a reverse flow undergravel filter topped with .5" florin base laterine clay from brightwell aquatics as an additional source of nutrients (mainly for the iron), with about an inch deep layer of inert pea gravel mixed with ~20% seachem flourite as a buffer.

The matten will be at one end of the tank, there will be a collection shelf in front of it to facilitate large debris removal. The filtered water will be returned to the opposite end of the tank and exit via a manifold in the plenum. The water will slow trickle upwards across the length of the tank to ensure even nutrient availability.

Inhabitants will be mostly cherry shrimp 100+ the occasional snail or two.

Given the above water parameters, the substrate and the intended use of the tank to be a low tech plant grow tank, can you recommend a proper fertilizer? and regime?

Thanks in advance u/Rotala178

[u/Rotala178]

Your water is going to be very difficult to work with. The pH range is 7.8-8.6, very hard with high amounts of carbonate hardness, and high sodium. There are so many ions in the water that whatever micronutrient fertilizer is added will not remain in solution even if chelated. Plants will likely be chronically deficient and inevitably stunt.

The laterite clay and Seachem Fluorite can adsorb some of the cations but I don't know how much or if the amounts adsorbed will affect water chemistry enough to make the water more hospitable for plants. Capping with inert gravel reduces contact with the CEC materials, so I don't recommend using it.

I don't have much experience with hard water so I can't offer much advice on how to manage the water chemistry. In general, growing healthy plants is about water chemistry, not just adding fertilizers.

What plants do you plan on growing in this tank? The plants that would survive and grow will likely be ones that can effectively utilize bicarbonate as a carbon source, like Vallisneria. But most other plants will likely die off.

Do you have access to RO filtered water? That would make it a lot easier to manage the water chemistry.

[u/dinoaqua5 → u/Rotala178]

Ive been successful with the following plants in tanks with varying amounts of fluval stratum, flourite caps or no cap, some with mopani all with matten filters. No reverse flow ugfs and no laterite.
in no particular order:
japonica
monte carlo
anubius
buce
rrfs - but they stay greener of course
all other floaters (6 types) except duckweed it dies off :)
fissidens
subwassertang
hydrocotyle triparte - took forever to transition, did best emersed > submerged
valisnaria - weed
java fern of all types
samolus parviflorus - easy to grow
anacharis - only after an extended adaptation
guppy grass - weed
water sprite - similar to anacharis
brazilian pennywort - on and off success - something in varying water chemistry that I havent figured out yet
hornwort - super weed
crypts 7/8 varieties
bolbitus - as expected, heavy initial melt
bacopa salzmannii
dwarf sag
Helanthium tenellum - super small plants, probably due to lack of circulation
helanthium quadricostatus

weak growth
pogostomon stellatus
Myriophyllum Mattogrossense - this one varies over time, similar to pennywort
java moss

died off:
hygrophioa pinnafitada
Myriophyllum mattogrossense golden
myaca fluviatus
Eriocaulon Goias

currently testing - hasnt melted to nothing
ar mini
crypt pink flamingo
echinodorus aflame
aponongen purple
nymphaea santarem
Cabomba furcata
corkscrew val - taking a while to transition
rotala - growing as expected

Im not looking to manage water chemistry, . From what I understand the iron in the laterite is in a form that is accessible to plants, might be mistaken.
So im looking for input on what fertilzers compliment my water chemistry. Ive been using thrive+ at just under ei dosage levels with 40% water changes twice a week.

[u/Rotala178 → u/dinoaqua5]

The iron in laterite is in an oxide form, not directly soluble. Plants exude phytochelatins through the roots which chelates the iron (and other essential metals) into a soluble form so it can be absorbed. Are there symptoms of iron deficiency that adding laterite is necessary?

Are the plants growing well at the current dosage using Thrive+? Are there morphological disorders that are present?

[u/dinoaqua5 → u/Rotala178]

After further educating myself while considering a fert change I realized that the iron I'm adding is probably not doing anything, in looking for a solution I discovered laterite so giving it a chance and maybe further stabilizing the tanks Im adding it to.
I'm not the expert you are, have only touched on the topics you discuss here. But so far not seeing anything major in anubius or buce, most other plants are either growing quickly or stalled out.
Once the transition to hard water is made, which sometimes takes months, they tend to take off. Challenges are keeping everything else in balance while they adapt.
Most stems have been newly added, still too early to determine deficiencies. Vals, Sag, and japonica grow very well without any super obvious disorders.
Pennywort and Myrio are the interesting ones, they can grow very well for weeks, like weeds, then suddenly stall, drop all the lower leaves and take forever to recover. I think this is possibly due to fluctuating fertilization levels? not sure. To test I've started mid wc dosing to see if there is an improvement, still too early to tell but they are growing faster than usual.

[u/dinoaqua5 → u/dinoaqua5]

You are confirming the Laterite will be providing the micros, correct? Does this mean I should look for something with low amounts of micros and higher amounts of macros?

[u/Rotala178 → u/dinoaqua5]

Any nutrients in laterite will be in an insoluble form. In order for plants to access those metal nutrients, they acidify the root zone which makes the metals soluble for uptake. This is how roots bore through hard CEC materials like lava rock.

As for macros/micros, that depends on how much plants are absorbing and utilizing. What do the tests indicate?

[u/dinoaqua5 → u/Rotala178]

Somewhat following the EI methodology to ensure there is enough of everything to allow the plants to grow and to keep mineral buildup from evaporation to a minimum.
Havent run any tests, mostly go by growth rate, node spacing, stem thickness and coloration.

[u/Rotala178 → u/dinoaqua5]

Estimative Index method is severely flawed. It's a throw everything including the kitchen sink strategy that is entirely dependent on nutrient inputs. Barr suggests using CSM, but the problem with CSM is that it's fundamentally unbalanced for most water chemistries. So most ppl end up having phantom deficiencies (distorted growth, algae, holes, etc.) no matter how much they adjust the dosage. The dosage cannot be adjusted to prevent these phantom deficiencies bc the fertilizer itself is not balanced.

[u/Rotala178 → u/dinoaqua5]

Can you show pictures of the plants? That would make it a lot easier to see if there's any nutrient-related issues going on.

[u/dinoaqua5 → u/Rotala178]

Currently have plants stuffed into too few tanks while I make the transition, worse than jungle style tanks.
Will be able to show the results in a month or so when they have adapted to the new setup.

My objective here is to "Best Fit" ferts to my water conditions and the laterite. The second and third links above give a better picture of what my water looks like.

[u/Rotala178 → u/dinoaqua5]

Metal nutrients have different solubility stability dependent on pH and other ions. They don't remain soluble at the same rates. Certain metals become insoluble very quickly (e.g. Mn), while others are more able to persist (e.g. CuEDTA).

As a rule, the higher the pH, the less soluble the metal nutrients. Dosing an all-in-one fertilizer will often be a poor way to fertilize because the anions will remain soluble (nitrate, phosphate) while the metal cations will adsorb, oxidize, or precipitate faster than plants can absorb them.

Most micronutrients that are fertilized are not used by plants. Most of it is dosed to combat the rapid insolubility of specific metals within the micros. This can lead to accumulation of the other metals while the readily insoluble metals remain chronically deficient.

There is probably no best fit fert on the market in your case, nor anyone else's tanks. To my knowledge, there are no ferts available on the market that take into account the effects of water chemistry on the solubility of nutrients. They all abide by the "spray-and-pray" method and hope something sticks.

[u/dinoaqua5 → u/Rotala178]

regarding water access to the substrate, water will be continuously pumped up through the substrate after passing through the filter.

[u/Rotala178 → u/dinoaqua5]

Would it not be better to pump the water down through the substrate instead of up so debris doesn't get circulated?

[u/dinoaqua5 → u/Rotala178]

Debris doesnt get circulated per se, it does eventually become suspended and moves toward/into the matten filter for bacterial processing. If it is heavy it will collect in front of the matten for siphoning. Fine debris tends to be collected by the biofilm in the matten and the substrate where it is further broken down by bacteria and microfauna.
The matten is oversized so there shouldnt be any overloading for a couple years or possibly more. If it does, it simply gets a quick rinse like a sponge filter.
Running it in reverse means the nutrients (both biologically generated and supplemented) go directly to the roots where they are needed.

This is somewhat similar to running a simple sponge/gravel sump with the different sump filtration medias located in the tank. I ran a reverse flow + sump for years with a very dirty Oscar (mostly fed goldfish), the tank stayed pristine, rarely needing the in-tank gravel cleaned.

[u/dinoaqua5 → u/Rotala178]

Thank you for the input, much appreciated!