How I Built 2 Niche Tools That Mainstream Sites Won't Touch (Fish Compatibility + Yarn Substitution)

David — Wed, 08 Jul 2026 03:47:08 +0000

Why These Markets?

Fish Compatibility Checker (AquaMateCheck)

Problem: Every fish compatibility site I found had low authority (DA 15-25). Fishori, TankBrain, AquariumStocking — all new sites, no traction.

Opportunity:

Google "can betta live with guppy" → first page has a forum post from 2014
No algorithm-based tools exist
All competitors are forum posts or static charts

My approach: Pairwise compatibility scoring based on 4 scientific parameters:

Temperature overlap (°F range intersection)
pH overlap (range intersection)
Temperament match (peaceful + peaceful = good)
Size predation risk (large mouth + tiny fish = predation)

Yarn Substitution Tool (StitchMatch)

Problem: Discontinued yarns are everywhere. Lion Brand "Homespun" (my grandma's favorite) was discontinued in 2023. People search for substitutes but find:

Random Reddit posts
Outdated blog posts from 2019
Forum threads with contradictory advice

Opportunity:

No DA 50+ site specializes in yarn substitution
Yarnize (DA 15-25) is new and low-authority
Search intent is clear: "yarn substitute for [brand] [name]"

My approach: Match based on 3 physical parameters:

Gauge (stitches per 4 inches) — most critical
Weight category (CYC 0-7 classification)
Yards per gram (yardage ratio)

Technical Architecture

pSEO Strategy

Fish Compatibility:

18 fish species → C(18,2) = 153 pairwise pages
Each page title matches search intent: "Can [Fish A] live with [Fish B]?"
Natural language titles = users search exactly this

Yarn Substitution:

15 yarns indexed → each yarn has a profile page
Discontinued yarns highlighted with ⚠️ badge
Top 5 substitutes ranked by gauge/weight/fiber match

Static Site Generator (Python)

Both projects use the same SSG pattern:

# build.py
from jinja2 import Environment, FileSystemLoader

def build_site():
    # Load JSON data
    fish_data = load_json("fish.json")

    # Generate pairwise pages
    for (slug_a, fish_a), (slug_b, fish_b) in combinations(fish_data.items(), 2):
        compatibility = calculate_compatibility(fish_a, fish_b)
        html = render("compatibility.html", {
            "fish_a": fish_a,
            "fish_b": fish_b,
            "compatibility": compatibility
        })
        write_html(f"compatibility/{slug_a}/{slug_b}", "index.html", html)

Zero dependencies — no Node.js, no npm, no React. Just Python + Jinja2.

Differentiated Design

Fish Compatibility (Deep Ocean Blue Theme)

Feature	Competitor	My Approach
Theme	Light generic	Deep ocean blue (#001a0f background)
Core Tool	Static chart	Quick Answer box + JS calculator
Data Source	Forum posts	FishBase.org (scientific database)
Methodology	Vague advice	4-step algorithmic scoring
EEAT Signal	None	Methodology section + FishBase citation

Key innovation: Water Parameter Overlap Table

Users see exact temperature/pH overlap (e.g., "72-78°F ✓ 6.5-7.5 ✓")
No vague "these fish might work"

Yarn Substitution (Morandi Warm Tone)

Feature	Competitor	My Approach
Theme	Modern minimalist	Warm craft aesthetic (#f5f3f0 background)
Core Tool	Basic search	Gauge + Weight + Fiber matching score
Discontinued Alert	No warning	⚠️ badge + "Discontinued" tag
Calculator	None	Yardage calculator (skein conversion)
Data Source	User submissions	Brand TDS sheets (official data)

Key innovation: Yardage Calculator

Pattern calls for 5 skeins of discontinued yarn → you need X skeins of substitute
Accounts for yards/gram ratio differences

Results After 1 Week

Fish Compatibility (jw-fishcheck.web.app)

Metric	Value
Pages Built	143 (153 pairs + 18 profiles + 3 tools + index)
Deploy Time	5 seconds (Firebase Hosting)
Zero Cost	Firebase free tier
SEO Structure	Clean URLs, sitemap, robots.txt

Yarn Substitution (jw-yarnswap.web.app)

Metric	Value
Pages Built	35 (15 profiles + 10 brands + 4 weights + calculator + index)
Deploy Time	5 seconds
Zero Cost	Firebase free tier

Lessons Learned

1. Blue Ocean Markets Are Real

Both markets have zero high-authority competitors. This is not theoretical:

Fish compatibility: All sites DA < 30
Yarn substitution: No dedicated site exists

Mainstream publishers avoid these niches because:

Brand safety: "Can Oscar eat Neon Tetra?" is violent content
Advertiser pressure: "Yarn substitute for discontinued brand" = product replacement (bad for advertisers)

2. pSEO > Manual Content

Pairwise generation creates natural search-intent titles:

"Can Betta live with Guppy?" = exactly what users search
"Red Heart Super Saver substitute" = exactly what users search

No keyword research needed — the titles ARE the keywords.

3. Static Sites Beat CMS

CMS Approach	Static Site Approach
Database query per page	Pre-generated HTML files
Server rendering	CDN-delivered static files
$10/month hosting	Firebase free tier
Slow TTFB	<100ms TTFB

4. Scientific Data > Forum Wisdom

Fish compatibility based on FishBase.org = authoritative.
Yarn substitution based on brand TDS = authoritative.

Users trust citations over "some guy on Reddit said..."

What's Next

Phase 1 (Completed)

✅ Fish compatibility: 18 species → 153 pairwise pages
✅ Yarn substitution: 15 yarns → profile pages + brand/weight categories
✅ Deployed to Firebase (JW account)
✅ Fixed 404 issues (added /fish/ and /yarn/ list pages)

Phase 2 (Planned)

Add 50+ fish species → C(50,2) = 1,225 compatibility pages
Add 100+ yarns → comprehensive substitution database
Add GSC verification + submit sitemaps
Monitor impressions/clicks after 30 days

Why This Approach Works

Zero competition: All mainstream sites avoid these topics
Clear search intent: Users search "can X live with Y" or "substitute for X"
Scientific data: FishBase + Brand TDS = authoritative sources
Static generation: Fast, free hosting, zero maintenance
pSEO scale: Pairwise pages = exponential growth without manual work

The lesson: Don't compete in crowded markets. Find niches where all competitors have DA < 30, then build authoritative tools with scientific data.

DEV Community: David