Goldfish are happy at almost any temperature. I kept them with tropicals at 78F with no problems for years. People who breed them keep them at room temperature, bumping it up byabout 5 degrees farenheit to induce spawning, sometimes lowering the temp to about 55F to simulate winter. As to how many you can put in a 135, it depends on a lot of things. There are many types, that I will put in 3 groups:
1)Common, Comet, Wakin, Wantonai, Bristol all grow to about a foot. I would not put in more than 3.
2)Ryukin, Jikin, ranchu, Lionhead, Vieltail, Oranda, Moor, Telescope, eggfish all grow to 6-9 inches. I would not put in more than 8.
3)Pearlscale, Tosakin, Bubbleeye, Celestial can't swim well, so although they are the same size as Ryukin, etc., I'd put in a few more.
I am very liberal with stocking, some people would cut the numbers in half, and say no group 1 fish in a 135. All fish from 1 are strong swimmers and may outcompete fish in 2&3 for food. All fish in 3 are delicate and may be hurt by more boisterous tankmates from the other two groups. Only fish from group 1 will take temperatures below 55F kindly. The plecos may eat the slime coating off the goldfish if they are underfed, so be careful. Also, goldfish do better with a little more greens in their diet, so a food for carnivorous cichlids shold be supplemented with cooked spinach or spirulina. Driftwood is OK, but if you raise the ph, the goldfish will have healthier fins. I'd keep the driftwood and throw some shells or coral sand into my sump/canister/hob. All sizes are for full grown fish. Many people buy a lot of small goldfish, and then give away/sell all but their favorites as they grow. Plants are hit or miss with goldfish, but the fancier the variety, the less it will like plants.
