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Guppies in planted tanks: 10+ gal, heater, plants as fry cover, mixed sexes = babies, and why they are not ‘easy’ if water and diet are ignored.

Corydoras in planted tanks: sand substrate, school of 6+, oxygen, no sharp gravel, gentle filter, and why they are not a ‘cleanup crew’ that lives on leftovers.

Betta splendens in planted tanks: 5+ gal heated, gentle filter, silk-soft plants, no sharp décor, cycling first, and tank mates that will not shred fins.

Water wisteria (Hygrophila difformis): fast easy stem, feathery submerged leaves, pinch and replant, low–medium light, optional CO₂, and lower-leaf melt fixes.

Amazon sword (Echinodorus): deep substrate, root tabs, medium light, melt after planting, and why it shades everything if you put it in a 10-gallon.

Rotala rotundifolia: medium–high light, CO₂ helps pink/orange tops, pinch often, and why it stays green and leggy in low-tech.

Hygrophila polysperma: fast low-tech stem, pinch tops, replant cuttings, medium light, optional CO₂, and how to stop lower-leaf melt and BBA.

Vallisneria spiralis / americana: plant the crown at substrate level, let runners fill the back, low–medium light, no CO₂ required, and how to stop melting after shipping.

Pond filters for goldfish/koi: pressurized vs waterfall, turnover about once per 1–2 hours, UV optional for green water, mechanical + biological media — not an aquarium HOB on a tub.

Carinotetraodon travancoricus: 5+ gal for one, 20+ for a group, snails + frozen foods, planted hardscape, not a community nano. Freshwater — not brackish.

Neocaridina (cherry) tolerate tap-range GH and breed easily. Caridina (bee/crystal) want RO + remineralizer and cooler, softer water. Do not mix colonies or copper.

Goldfish listing or floating after flakes is usually constipation and swallowed air — not mystery “swim bladder disease.” Fast, pea or gel food, sinking pellets, cool clean water.

Honest under-$100 fancy goldfish start: 20+ gallon used tank, sponge filter, gravel vac, sinking pellets — not a bowl, not a 5-gallon kit.