Can Siamese fighting fish Live With Guppy?

Long-finned fish are the one group to rule out with a betta. Species with trailing finnage should certainly be avoided, because a male betta may view them as rivals, and male guppies carry exactly that kind of long, flowing tail.

Water chemistry would not stop you. Guppies take 17 to 28 °C at pH 7 to 8 and a betta manages 22 to 30 °C at pH 6 to 8, so a tank around 24 to 28 °C and pH 7 to 8 suits both on paper. The conflict is behaviour, not chemistry.

Keep them in separate tanks. Guppies do well in a quiet community with other livebearers, rasboras, corydoras, small loricariids and tetras, and a betta is best kept on its own. Plan the guppy tank for growth, too: females give birth to fully formed fry every 25 to 30 days, and dense planting lets some of them survive.